I just created a Mountain Lion guest on my new iMac running on Yosemite in order to run old software (e.g. iWeb). The machine is running well but I have a strange bug occurring that actually prevents me of using iWeb. In certains menus or programs, and in particular in iWeb, the actual web pages do not show, but the objects do exist, if I click and drag an image for example, it is moved, but nothing actually appears. The same behavior occurs in the users and groups in the preferences pane, if I change the user image, the selection menu is grey, but if I double click in it, I can actually select an invisible picture! Any suggestions or solutions?