diff --git a/src/calibre/gui2/dialogs/tag_categories.py b/src/calibre/gui2/dialogs/tag_categories.py
index 9bddb817cf..899d3d1920 100644
--- a/src/calibre/gui2/dialogs/tag_categories.py
+++ b/src/calibre/gui2/dialogs/tag_categories.py
@@ -178,8 +178,10 @@ class TagCategories(QDialog, Ui_TagCategories):
                       'multiple periods in a row or spaces before '
                       'or after periods.')).exec_()
             return False
-        for c in self.categories:
-            if strcmp(c, cat_name) == 0:
+        for c in sorted(self.categories.keys(), key=sort_key):
+            if strcmp(c, cat_name) == 0 or \
+                    (icu_lower(cat_name).startswith(icu_lower(c) + '.') and\
+                     not cat_name.startswith(c + '.')):
                 error_dialog(self, _('Name already used'),
                         _('That name is already used, perhaps with different case.')).exec_()
                 return False
diff --git a/src/calibre/gui2/search_box.py b/src/calibre/gui2/search_box.py
index 34be6cd276..5a4c34a5cd 100644
--- a/src/calibre/gui2/search_box.py
+++ b/src/calibre/gui2/search_box.py
@@ -217,11 +217,15 @@ class SearchBox2(QComboBox): # {{{
                 self.clear()
             else:
                 self.normalize_state()
+                self.lineEdit().setCompleter(None)
                 self.setEditText(txt)
                 self.line_edit.end(False)
                 if emit_changed:
                     self.changed.emit()
                 self._do_search(store_in_history=store_in_history)
+                c = QCompleter()
+                self.lineEdit().setCompleter(c)
+                c.setCompletionMode(c.PopupCompletion)
             self.focus_to_library.emit()
         finally:
             if not store_in_history:
diff --git a/src/calibre/gui2/tag_view.py b/src/calibre/gui2/tag_view.py
index 034d88e02d..5986717753 100644
--- a/src/calibre/gui2/tag_view.py
+++ b/src/calibre/gui2/tag_view.py
@@ -654,7 +654,6 @@ class TagTreeItem(object): # {{{
         '''
         set_to: None => advance the state, otherwise a value from TAG_SEARCH_STATES
         '''
-#        if self.type == self.TAG:
         if set_to is None:
             while True:
                 self.tag.state = (self.tag.state + 1)%5
@@ -1319,16 +1318,19 @@ class TagsModel(QAbstractItemModel): # {{{
                 return False
 
             user_cats = self.db.prefs.get('user_categories', {})
+            user_cat_keys_lower = [icu_lower(k) for k in user_cats]
             ckey = item.category_key[1:]
+            ckey_lower = icu_lower(ckey)
             dotpos = ckey.rfind('.')
             if dotpos < 0:
                 nkey = val
             else:
                 nkey = ckey[:dotpos+1] + val
-            for c in user_cats:
-                if c.startswith(ckey):
+            nkey_lower = icu_lower(nkey)
+            for c in sorted(user_cats.keys(), key=sort_key):
+                if icu_lower(c).startswith(ckey_lower):
                     if len(c) == len(ckey):
-                        if nkey in user_cats:
+                        if nkey_lower in user_cat_keys_lower:
                             error_dialog(self.tags_view, _('Rename user category'),
                                 _('The name %s is already used')%nkey, show=True)
                             return False
@@ -1336,7 +1338,7 @@ class TagsModel(QAbstractItemModel): # {{{
                         del user_cats[ckey]
                     elif c[len(ckey)] == '.':
                         rest = c[len(ckey):]
-                        if (nkey + rest) in user_cats:
+                        if icu_lower(nkey + rest) in user_cat_keys_lower:
                             error_dialog(self.tags_view, _('Rename user category'),
                                 _('The name %s is already used')%(nkey+rest), show=True)
                             return False
@@ -1512,7 +1514,6 @@ class TagsModel(QAbstractItemModel): # {{{
     def reset_all_states(self, except_=None):
         update_list = []
         def process_tag(tag_item):
-#            if tag_item.type != TagTreeItem.CATEGORY:
             tag = tag_item.tag
             if tag is except_:
                 tag_index = self.createIndex(tag_item.row(), 0, tag_item)