Layer mask filled with blocks
Mulitple times over the last year or so I have had layer masks corrupt and fill with random block patterns. It tends to happen on large files with lots of layers. It can happen to multiple layers at the same time. Only way to get orignal mask back is to make a selction (CMD+Click), invert that selection and fill with black.
Very annoying!
My files are generally 16bit and PSB's if that makes any difference.


