I just had the same problem, C4D blanked some textures I painted with bodypaint, (and then obviously saved in a psd file), I did have autosave activated but it was useless anyway since psd textures are not saved automatically by cinema 4d, I was working with bodypaint with another texture on another object, when i finished I found out C4D blackened 3 textures I did a few hours before.
Now after several curses and hours of work lost I gave up on retrieving my textures, but I’d only like to know what went wrong inside the program…