Found a cause of the ntdll.dll crashout (for me at least). It's seems to be something to do with re-sizing documents down to either 180 or 181 pixels in width (images can be larger and re-sized 'down' or smaller and sized 'up', still causes the same problem). Affects both blank and layered documents, although for the latter, if the layers remain untouched after re-sizing it can be saved, move an object, re-save and Photo-Paint locks up.
If you don't have any issues with PP then this probably can't re replicated, if you are then try tha above and see what happens.
Full explanation and fix can be found here - https://www.katsbits.com/smforum/index.php?topic=359.0. Random third-party generic 'scan and fix' programs won't solve this problem, especially given that Windows 8, 8.1 and 10 change the behaviour of this problem.