diff --git a/resources/recipes/azstarnet.recipe b/resources/recipes/azstarnet.recipe
index 6113f84d40..45339ae208 100644
--- a/resources/recipes/azstarnet.recipe
+++ b/resources/recipes/azstarnet.recipe
@@ -41,7 +41,7 @@ class Azstarnet(BasicNewsRecipe):
                                    })
             br.open('http://azstarnet.com/app/registration/proxy.php',data)
         return br
-                        
+
     remove_tags = [dict(name=['object','link','iframe','base','img'])]
 
 
diff --git a/src/calibre/customize/ui.py b/src/calibre/customize/ui.py
index c544419b06..0f072d1f70 100644
--- a/src/calibre/customize/ui.py
+++ b/src/calibre/customize/ui.py
@@ -235,6 +235,8 @@ def _run_filetype_plugins(path_to_file, ft=None, occasion='preprocess'):
         with plugin:
             try:
                 nfp = plugin.run(path_to_file)
+                if not nfp:
+                    nfp = path_to_file
             except:
                 print 'Running file type plugin %s failed with traceback:'%plugin.name
                 traceback.print_exc()
diff --git a/src/calibre/ebooks/__init__.py b/src/calibre/ebooks/__init__.py
index 38a8ef3662..0b3d6b901a 100644
--- a/src/calibre/ebooks/__init__.py
+++ b/src/calibre/ebooks/__init__.py
@@ -129,3 +129,11 @@ def render_html(path_to_html, width=590, height=750):
     del loop
     return renderer
 
+def check_ebook_format(stream, current_guess):
+    ans = current_guess
+    if current_guess.lower() in ('prc', 'mobi', 'azw', 'azw1'):
+        stream.seek(0)
+        if stream.read(3) == 'TPZ':
+            ans = 'tpz'
+    return ans
+
diff --git a/src/calibre/ebooks/mobi/reader.py b/src/calibre/ebooks/mobi/reader.py
index ed61dbd719..146fdf983c 100644
--- a/src/calibre/ebooks/mobi/reader.py
+++ b/src/calibre/ebooks/mobi/reader.py
@@ -798,44 +798,40 @@ def get_metadata(stream):
     from calibre.utils.logging import Log
     log = Log()
     mi = MetaInformation(os.path.basename(stream.name), [_('Unknown')])
-    try:
-        mh = MetadataHeader(stream, log)
-        if mh.title and mh.title != _('Unknown'):
-            mi.title = mh.title
+    mh = MetadataHeader(stream, log)
+    if mh.title and mh.title != _('Unknown'):
+        mi.title = mh.title
 
-        if mh.exth is not None:
-            if mh.exth.mi is not None:
-                mi = mh.exth.mi
-        else:
-            size = sys.maxint
-            if hasattr(stream, 'seek') and hasattr(stream, 'tell'):
-                pos = stream.tell()
-                stream.seek(0, 2)
-                size = stream.tell()
-                stream.seek(pos)
-            if size < 4*1024*1024:
-                with TemporaryDirectory('_mobi_meta_reader') as tdir:
-                    with CurrentDir(tdir):
-                        mr = MobiReader(stream, log)
-                        parse_cache = {}
-                        mr.extract_content(tdir, parse_cache)
-                        if mr.embedded_mi is not None:
-                            mi = mr.embedded_mi
-        if hasattr(mh.exth, 'cover_offset'):
-            cover_index = mh.first_image_index + mh.exth.cover_offset
-            data  = mh.section_data(int(cover_index))
-        else:
-            data  = mh.section_data(mh.first_image_index)
-        buf = cStringIO.StringIO(data)
-        try:
-            im = PILImage.open(buf)
-        except:
-            log.exception('Failed to read MOBI cover')
-        else:
-            obuf = cStringIO.StringIO()
-            im.convert('RGB').save(obuf, format='JPEG')
-            mi.cover_data = ('jpg', obuf.getvalue())
+    if mh.exth is not None:
+        if mh.exth.mi is not None:
+            mi = mh.exth.mi
+    else:
+        size = sys.maxint
+        if hasattr(stream, 'seek') and hasattr(stream, 'tell'):
+            pos = stream.tell()
+            stream.seek(0, 2)
+            size = stream.tell()
+            stream.seek(pos)
+        if size < 4*1024*1024:
+            with TemporaryDirectory('_mobi_meta_reader') as tdir:
+                with CurrentDir(tdir):
+                    mr = MobiReader(stream, log)
+                    parse_cache = {}
+                    mr.extract_content(tdir, parse_cache)
+                    if mr.embedded_mi is not None:
+                        mi = mr.embedded_mi
+    if hasattr(mh.exth, 'cover_offset'):
+        cover_index = mh.first_image_index + mh.exth.cover_offset
+        data  = mh.section_data(int(cover_index))
+    else:
+        data  = mh.section_data(mh.first_image_index)
+    buf = cStringIO.StringIO(data)
+    try:
+        im = PILImage.open(buf)
     except:
-        log.filter_level = Log.DEBUG
-        log.exception('Failed to read MOBI metadata')
+        log.exception('Failed to read MOBI cover')
+    else:
+        obuf = cStringIO.StringIO()
+        im.convert('RGB').save(obuf, format='JPEG')
+        mi.cover_data = ('jpg', obuf.getvalue())
     return mi
diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index 6ccb7363ec..6938628759 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -34,7 +34,7 @@ from calibre.customize.ui import run_plugins_on_import
 
 from calibre.utils.filenames import ascii_filename
 from calibre.utils.date import utcnow, now as nowf, utcfromtimestamp
-from calibre.ebooks import BOOK_EXTENSIONS
+from calibre.ebooks import BOOK_EXTENSIONS, check_ebook_format
 
 if iswindows:
     import calibre.utils.winshell as winshell
@@ -993,7 +993,9 @@ class LibraryDatabase2(LibraryDatabase):
                               path=None, notify=True):
         npath = self.run_import_plugins(fpath, format)
         format = os.path.splitext(npath)[-1].lower().replace('.', '').upper()
-        return self.add_format(index, format, open(npath, 'rb'),
+        stream = open(npath, 'rb')
+        format = check_ebook_format(stream, format)
+        return self.add_format(index, format, stream,
                                index_is_id=index_is_id, path=path, notify=notify)
 
     def add_format(self, index, format, stream, index_is_id=False, path=None, notify=True):
@@ -1596,6 +1598,7 @@ class LibraryDatabase2(LibraryDatabase):
             npath = self.run_import_plugins(path, format)
             format = os.path.splitext(npath)[-1].lower().replace('.', '').upper()
             stream = open(npath, 'rb')
+            format = check_ebook_format(stream, format)
             self.add_format(id, format, stream, index_is_id=True)
             stream.close()
         self.conn.commit()