Sometimes when I use Photoshop, the "text" in the software disappears completely. Like, if I press "File" (which is still visible on my iMac), I get a completely blank box staring at me. The text is there, because if I hover over where "Save" would be and press it, the "Save" box appears, also blank, but I can't see any text! This is extremely annoying, what's wrong? I have to restart Photoshop, and then it's fine again.