Cropping animating background hangs in safari

I’ve build some flash websites that call a javascript function that crops the website. Some of these website has got animating backgrounds.

On some macs in safari, the .swf hangs when cropping the movie (but only if the movie has an animating background). This does not happen on all macs (though flash/safari version are the same). When clicking the mouse in the browser, the flash movie usually continues for a few seconds before hanging again.

I’ve tried hiding the animation (with a graphic), but this doesn’t seem to work. Disabling the animation does work. This problem occurs in several flash websites I’ve build, with different kinds of animations.

Does anybody know about this, and knows how to fix it?