Google ads with mouse over effect

Just seen on a simple forum site

[jetteroheller]

I moved the mouse over a 300x250 Adsense block,
when one of the 3 ads in the 300x250 changed background color.

I tested this, all 3 ads in the block have mouse over effects.
The background color of the ad changes.

It's a simple forum, so I assume it's not a premium publisher

[zarathustra2011]

All my text ads have that roll over effect - I assumed it was just the default standard, unless I'm missing something?

[DaStarBuG]

Noticed that a while ago too.
However it only works in IE not in Firefox, at least for me.

[zarathustra2011]

Works in Google Chrome too, but not Opera.