Since at least version 8, Internet Explorer has had an unfeature called "accelerators". It becomes manifest when you mark a bit of text on a web page, disrupting useful features such as copy/paste or marking text using Ctrl/Shift arrow keys.
[Update 01.11.14: I just discovered a feature in IE11 that is accessible via »Ansicht -> Tastaturnavigation« (probably »View -> Keyboard Navigation« in English) allowing you to select text for copy/paste using the keyboard. It is also accessible via F7.]
It seems that back in version 8, the way to remove this horrible unfeature is to remove each and every "accelerator", which can be done using the add-on manager. (See What is the blue double arrow that appears over links? for some pointers.) But now in 11, this does not seem to do the trick any more. I have removed them all and restarted IE and the nasty unfeature keeps rearing its ugly blue double-arrow head. How to kill the beast?