Working on a site tonight and I found that if you try to Buttonize an object that was already set with Mouseover properties the program immediately crashes. Did this action twice in a row by dumb luck before I realized what was causing it. Then I was able to open up the site again and purposely do it. Not sure if this will occur on all machines or not, but it happens on mine!
Vista Ultimate
VSD 7.0 build 11, registered
IE 8

It didn't crash when I tried the same. Not even when I had both the mouseover object and the buttonized one intersecting. I just got a warning that they were intersecting and was asked to move one of the objects. After I did that, both the mouseover and the button behaved as they were supposed to.

Win7 home premium, FF3.6.13 and IE8, VSD 7.0 build 11, registered

I tried it and it didn't crash. I tried a couple of different ways by buttonizing before save and after save.

These were objects on a site I had to open from a backup file, which may be why this happened. I had a few images that were set as Mouseover objects in the previous file. When I tried to Buttonize one, immediate crash. Second time same thing. Intentional next time and .... crash.
But I am glad to hear it is not happening on other computers!