JS error when switching to source mode under specific conditions

[Freddie Bingham]

Humor me with this one.

This involves a nested form and nested forms are not valid. Regardless, that does not explain why I am having this problem. You know it is possible to start with a single form, nest a form via javascript (Move Editor below), extract data via javascript, and be perfectly well with it. It only happens in IE7 and IE8, IE9 is happy.

1. Load the sample
2. Press "Create Editor".
3. Press "Move Editor".
4. Press "Source"

This recreates a scenario that I am having issues with. Here you will receive a JS error emanating from the richcombo plugin. The following event is fired on mode changes and it is the 'setValue' call below that is the cause of the problem.

editor.on( 'mode', function()
	{
		this.setState( this.modes[ editor.mode ] ? CKEDITOR.TRISTATE_OFF : CKEDITOR.TRISTATE_DISABLED );
		this.setValue( '' );
	},
	this );

[Freddie Bingham]

Sample file, modified from the sample in the download. Just overwrite the existing file of the same name and open in IE8

[Jakub Ś]

Since it is invalid HTML, browser can interpret it differently. I'm not convinced if CKEditor is the one to blame.

Reproducible in IE6, IE7 and IE8.

The JS error that is thrown is:
Message: Unknown runtime error
Line: 379
Char: 4
URI: /ckeditor/_source/core/dom/element.js

[Jakub Ś]

I think the reason for this bug may have been described in #8590.

This may be because IE6-8 are the only browsers which don't remove the nested form tags which as @fbingha has already mentioned is invalid HTML.