Problems using image acquistion toolbox with AVT Guppy camera (firewire) and DCAM driver.

I recognised a strange effect, when working with a firewire camera on OsX 10.6 with Matlab 2011a. When I start the image acquisition tool and choose one of the available dcam-modes and start and stop the preview a few times I recently get the following error: "The attempt to preview failed. The error was: Error using ==> imaqdevice.preview at 181 dcam: Unable to set the bytes per packet on the camera." I can click the error away and restart the preview, which then works again. Some similar behaviour is recognisable, when accessing the camera by a script. Does anybody know this strange behaviour? For me it looks as there is a bug in the image acquisition toolbox for os x?