I wish I could, I have tried to reproduce this, but so far no luck. What I basically did was:
I opened a .png image
I opened a .pdn image where I copied a whole layer (with a grid).
I added a new layer
I pasted the grid there.
I worked on it for a few hours. Mostly have been using the pencil tool. Sometimes the color picker, line tool, move selected pixels (copy pasting), and zoom tool.
Most of the time I hide the grid layer, and while trying to save, the grid layer was hidden too.
I probably used the pencil tool last, however it might also have been the line tool, move selected pixels, or the zoom tool. I probably did not use the color picker last. I'm sure that while editing I have not used these tools: lasso select, ellipse select, magic wand, gradient, eraser, clone stamp, recolor, text and shapes.
I tried to save it under a different name (as .png)
I have not changed any of the quality options.
It's quite hard for me to remember what I did, since I did not expect it to crash (I never had any crashes with pdn before) and was not really paying attention to what I doing exactly. Also while trying to reproduce the bug, it did not crash anymore. I hope this helps.