* Fixed bug where syntax highlighting was lost after updating a prompt with a bad number.

* Minor cleanup and bug fix to ConsoleWidget's _insert_html_fetching_plain_text

IPython/frontend/qt/console/console_widget.py

@@ -893,12 +893,17 b' class ConsoleWidget(QtGui.QWidget):'
         """ Inserts HTML using the specified cursor, then returns its plain text
             version.
         """
+        cursor.beginEditBlock()
+        cursor.removeSelectedText()
+
         start = cursor.position()
         self._insert_html(cursor, html)
         end = cursor.position()
         cursor.setPosition(start, QtGui.QTextCursor.KeepAnchor)
         text = str(cursor.selection().toPlainText())
+
         cursor.setPosition(end)
+        cursor.endEditBlock()
         return text
 
     def _insert_plain_text(self, cursor, text):

IPython/frontend/qt/console/frontend_widget.py

@@ -69,6 +69,10 b' class FrontendWidget(HistoryConsoleWidget, BaseFrontendMixin):'
     # processed by the FrontendWidget.
     executed = QtCore.pyqtSignal(object)
 
+    # Protected class attributes.
+    _highlighter_class = FrontendHighlighter
+    _input_splitter_class = InputSplitter
+
     #---------------------------------------------------------------------------
     # 'object' interface
     #---------------------------------------------------------------------------
@@ -80,8 +84,8 b' class FrontendWidget(HistoryConsoleWidget, BaseFrontendMixin):'
         self._call_tip_widget = CallTipWidget(self._control)
         self._completion_lexer = CompletionLexer(PythonLexer())
         self._hidden = True
-        self._highlighter = FrontendHighlighter(self)
-        self._input_splitter = InputSplitter(input_mode='replace')
+        self._highlighter = self._highlighter_class(self)
+        self._input_splitter = self._input_splitter_class(input_mode='replace')
         self._kernel_manager = None
 
         # Configure the ConsoleWidget.

IPython/frontend/qt/console/ipython_widget.py

@@ -51,6 +51,9 b' class IPythonWidget(FrontendWidget):'
     in_prompt = '<br/>In [<span class="in-prompt-number">%i</span>]: '
     out_prompt = 'Out[<span class="out-prompt-number">%i</span>]: '
 
+    # FrontendWidget protected class attributes.
+    #_input_splitter_class = IPythonInputSplitter
+
     #---------------------------------------------------------------------------
     # 'object' interface
     #---------------------------------------------------------------------------
@@ -58,9 +61,6 b' class IPythonWidget(FrontendWidget):'
     def __init__(self, *args, **kw):
         super(IPythonWidget, self).__init__(*args, **kw)
 
-        # FrontendWidget protected variables.
-        #self._input_splitter = IPythonInputSplitter(input_mode='replace')
-
         # IPythonWidget protected variables.
         self._previous_prompt_obj = None
 
@@ -141,12 +141,23 b' class IPythonWidget(FrontendWidget):'
                 self._previous_prompt_obj.number != previous_prompt_number:
             block = self._previous_prompt_obj.block
             if block.isValid():
+
+                # Remove the old prompt and insert a new prompt.
                 cursor = QtGui.QTextCursor(block)
                 cursor.movePosition(QtGui.QTextCursor.Right,
                                     QtGui.QTextCursor.KeepAnchor, 
                                     self._previous_prompt_obj.length)
                 prompt = self._make_in_prompt(previous_prompt_number)
-                self._insert_html(cursor, prompt)
+                self._prompt = self._insert_html_fetching_plain_text(
+                    cursor, prompt)
+
+                # XXX: When the HTML is inserted, Qt blows away the syntax
+                #      highlighting for the line. I cannot for the life of me
+                #      determine how to preserve the existing formatting.
+                self._highlighter.highlighting_on = True
+                self._highlighter.rehighlightBlock(cursor.block())
+                self._highlighter.highlighting_on = False
+
             self._previous_prompt_obj = None
 
         # Show a new prompt with the kernel's estimated prompt number.