FF: Can't apply styles after removing line

[j.swiderski]

To reproduce:

1. Open replacebycode sample
2. Click inside editor and press CRTL+A
3. Press backspace few times quickly Two is usually enough but you may need to press it few more times. Cursor should go up a little bit.
4. Try to apply style from styles dorpdown like Blue, Red title, big, Small (it works with some styles) or underline, subscript, superscript, strike (it works with bold and italic).

Result: Cursor will go up a little bit and style/button won't get applied/activated.

Reproducible in Firefox from CKEditor 3.5.3

[j.swiderski]

reproducible from CKE 3.5.3 rev. [6586]