I don't think there'd be a limitation on this. Do you have a sample?
What are kind of sample are you looking for?
Either the Fireworks PNG or a link to an exported HTML version.
Here are the links.
The first button 'Account Managers' is supposed to swap.
It sopped swapping when I added the swap image behavior to 'Reports'
On other tests I did with many files starting from scratch I got the same results also,
as I added buttons more swap behaviors detached sequentialy i.e. 'Auctions Raffles was the next button to stop swapping.
Thanks for your help with this. I am launching a new version of our software and would like to have 12 buttons with disjointed rollovers if possible.