Firefox: Additional </br> added after clicking legend in fieldset and switching to Source mode

[krst]

When focus is set in legend of a fieldset, and then mode is switched to source and back, additional </BR> is added to fieldset.

Environment

linked with #6804 , Firefox 4/5b

TC

1. Paste following code into editor

   <fieldset> <legend>caption</legend> <p>keep going, CKeditor!</p> </fieldset>
   

2. Switch mode to WYSIWYG
3. Set caret in "caption"
4. Switch to source
5. Repeat steps 2-4, two times

Actual result

Additional </br> added

<fieldset>
	<legend>caption</legend><br />
	<br />
	<br />
	<p>
		keep going, CKeditor!</p>
</fieldset>

[j.swiderski]

This is reproducible in Firefox 3.6 and 4.

Every time you place the cursor next to a different letter inside "caption" and switch to source the new <br> will be inserted.