rollover state for image in text area

Hi I have used code like the bit below successfully in the footer widget at this domain: http://kristencooper.com/ctt/

To make a mouseover rollover state.

However, when I use similar code to make a rollover state for a button in a text block on a page made with the advanced editor, I find when I save the page and reopen it the code mostly vanishes and it doesn’t work. Can a text block not accept code like that in text view mode?

I have this for a single image and it works fine:

But add the rollover code and the text block won’t take it after a save. Is that something I just can’t do there? Any help would be mucho appreciated.

Thanks,

Tony