diff --git a/src/calibre/debug.py b/src/calibre/debug.py
index 66de8ccadb..d1e97efe2a 100644
--- a/src/calibre/debug.py
+++ b/src/calibre/debug.py
@@ -191,6 +191,8 @@ def main(args=sys.argv):
         exec opts.command
     elif opts.exec_file:
         sys.argv = args[:1]
+        base = os.path.dirname(os.path.abspath(opts.exec_file))
+        sys.path.insert(0, base)
         execfile(opts.exec_file)
     elif opts.debug_device_driver:
         debug_device_driver()
diff --git a/src/calibre/gui2/convert/__init__.py b/src/calibre/gui2/convert/__init__.py
index 5022a2ae76..383fe2d36f 100644
--- a/src/calibre/gui2/convert/__init__.py
+++ b/src/calibre/gui2/convert/__init__.py
@@ -164,6 +164,9 @@ class Widget(QWidget):
     def post_get_value(self, g):
         pass
 
+    def break_cycles(self):
+        self.db = None
+
     def pre_commit_check(self):
         return True
 
diff --git a/src/calibre/gui2/convert/single.py b/src/calibre/gui2/convert/single.py
index 2f05d50a7f..d14f5c905d 100644
--- a/src/calibre/gui2/convert/single.py
+++ b/src/calibre/gui2/convert/single.py
@@ -115,7 +115,6 @@ class Config(ResizableDialog, Ui_Dialog):
     def __init__(self, parent, db, book_id,
             preferred_input_format=None, preferred_output_format=None):
         ResizableDialog.__init__(self, parent)
-
         self.setup_input_output_formats(db, book_id, preferred_input_format,
                 preferred_output_format)
         self.db, self.book_id = db, book_id
@@ -248,8 +247,18 @@ class Config(ResizableDialog, Ui_Dialog):
         if self.db is not None:
             recs['gui_preferred_input_format'] = self.input_format
             save_specifics(self.db, self.book_id, recs)
+        self.break_cycles()
         ResizableDialog.accept(self)
 
+    def reject(self):
+        self.break_cycles()
+        ResizableDialog.reject(self)
+
+    def break_cycles(self):
+        for i in range(self.stack.count()):
+            w = self.stack.widget(i)
+            w.break_cycles()
+
     @property
     def recommendations(self):
         recs = [(k, v, OptionRecommendation.HIGH) for k, v in
diff --git a/src/calibre/gui2/convert/structure_detection.py b/src/calibre/gui2/convert/structure_detection.py
index c109b200be..1797a76760 100644
--- a/src/calibre/gui2/convert/structure_detection.py
+++ b/src/calibre/gui2/convert/structure_detection.py
@@ -41,6 +41,11 @@ class StructureDetectionWidget(Widget, Ui_Form):
         self.opt_footer_regex.set_book_id(book_id)
         self.opt_footer_regex.set_db(db)
 
+    def break_cycles(self):
+        Widget.break_cycles(self)
+        self.opt_header_regex.db = None
+        self.opt_footer_regex.db = None
+
     def pre_commit_check(self):
         for x in ('header_regex', 'footer_regex'):
             x = getattr(self, 'opt_'+x)
diff --git a/src/calibre/gui2/tools.py b/src/calibre/gui2/tools.py
index 8ffaceaa64..26a417555a 100644
--- a/src/calibre/gui2/tools.py
+++ b/src/calibre/gui2/tools.py
@@ -77,6 +77,7 @@ def convert_single_ebook(parent, db, book_ids, auto_conversion=False, out_format
                 jobs.append(('gui_convert', args, desc, d.output_format.upper(), book_id, temp_files))
 
                 changed = True
+                d.break_cycles()
         except NoSupportedInputFormats:
             bad.append(book_id)