diff --git a/qutebrowser/config/config.py b/qutebrowser/config/config.py
index 1a24f6c61..43b9db257 100644
--- a/qutebrowser/config/config.py
+++ b/qutebrowser/config/config.py
@@ -18,12 +18,10 @@
 """Configuration storage and config-related utilities."""
 
 import os
-import io
 import os.path
 import logging
 import textwrap
-from configparser import (ConfigParser, ExtendedInterpolation, NoSectionError,
-                          NoOptionError)
+from configparser import ConfigParser, ExtendedInterpolation
 
 #from qutebrowser.utils.misc import read_file
 import qutebrowser.config.configdata as configdata
diff --git a/qutebrowser/models/completion.py b/qutebrowser/models/completion.py
index 16e72372d..d12968f55 100644
--- a/qutebrowser/models/completion.py
+++ b/qutebrowser/models/completion.py
@@ -271,8 +271,10 @@ class CompletionModel(QAbstractItemModel):
 
         """
         if parent.model() is not None and parent.model() is not self:
-            logging.debug("row {}, column {}, parent {}, parentmodel {}, self {}".format(row, column, parent, parent.model(), self))
-            from qutebrowser.utils.debug import set_trace; set_trace()
+            logging.warn("index() called with wrong parent! - "
+                         "row {}, column {}, parentmodel {}, self {}".format(
+                             row, column, parent.model(), self))
+            return
         if (0 <= row < self.rowCount(parent) and
                 0 <= column < self.columnCount(parent)):
             pass
diff --git a/qutebrowser/models/completionfilter.py b/qutebrowser/models/completionfilter.py
index 55e5815e6..0ba6709be 100644
--- a/qutebrowser/models/completionfilter.py
+++ b/qutebrowser/models/completionfilter.py
@@ -79,6 +79,7 @@ class CompletionFilterModel(QSortFilterProxyModel):
         return self.index(self.rowCount(cat) - 1, 0, cat)
 
     def setSourceModel(self, model):
+        """Override QSortFilterProxyModel's setSourceModel to clear pattern."""
         logging.debug("Setting source model: {}".format(model))
         self.pattern = ''
         super().setSourceModel(model)