UndoRedo flooding causes scene to misbehave and crash. #35

How to reproduce

Start the GUI. Add about 20 logic items. Enable the History.
Then click on an element on the history, keep the mouse pressed and move the cursor up and down very quickly for several seconds. This will rewind and replay the complete history step by step as fast as possible.
At some point the GUI starts to slow down and soon stops to respond. This is expected, so stop the action and wait a few seconds.

The problem

At this point try to select some items in the scene. You will notice that the selection is broken (no selection rectangles are shown). Also notice, the application continuously draws 100% CPU utilization at this point, without being clear on what it is doing.