After disabling the contextmenu plugin, native context menu on a selection is broken in IE7 and IE8

[Matthias]

The native context menu is broken in IE 7 and IE 8 without contextmenu plugin when a selection exists.

Steps to reproduce (in my real live application I removed all UI, menu, etc. plugins):

• Disable the contextmenu plugin:
  • remove contextmenu and scayt entry in plugins list in _source/core/config.js
    • remove contextmenu in requires block in _source/plugins/menubutton/plugin.js
    • disable contextmenu usage in _source/plugins/menubutton/plugin.js e.g. by changing "if ( !menu )" to "if ( false )" (this is just an example... as I said in my app I disabled the menubutton plugin completely... This is just for demonstration of the bug)
• Change the samples to use the source (e.g. _samples/replacebyclass.html: replace ckeditor.js with ckeditor_source.js)
• Start the sample (e.g _samples/replacebyclass.html) in IE 8
• write some words
• select one word
• right click on the selected word

=> Result: the selection disappears, the cut, copy, etc. buttons are disabled. If you select one of the other elements (e.g. Select All) the selected text is removed! If you select nothing in the context menu and click back into the editor, the selection is restored!

I suppose this is some kind of strange focus bug, that only seems to occur in IE 7 and IE 8 (in IE 6, FF, Chrome, ... it works)