HTMLZ: metadata replace metadata after merging. APNX don't use tag starting with d as paragraph tag as it breaks more than it fixes.

src/calibre/devices/kindle/apnx.py

@@ -164,7 +164,7 @@ class APNXBuilder(object):
                 if c == '/':
                     closing = True
                     continue
-                elif c in ('d', 'p'):
+                elif c == 'p':
                     if closing:
                         in_p = False
                     else:

src/calibre/ebooks/metadata/extz.py

@@ -70,7 +70,7 @@ def set_metadata(stream, mi):
     # Update the metadata.
     old_mi = opf.to_book_metadata()
     old_mi.smart_update(mi)
-    opf.smart_update(metadata_to_opf(old_mi))
+    opf.smart_update(metadata_to_opf(old_mi), replace_metadata=True)
     newopf = StringIO(opf.render())
     safe_replace(stream, opf_path, newopf, extra_replacements=replacements, add_missing=True)