Richard,

Unfortunately, the problem is verified random.

Start with file A. Copy to A-copy. Make 1 complicated change (e.g. inversion that covers a range of non-contiguous regions, nodes, cnodes, etc.) Undo, and certain carry-forward parameters aren't handled correctly, as well as nodes/cnodes.

Close the file without saving and repeat. No problem.

Delete A-copy and recreate A-copy from A. Still no problem.

Maybe it's a reserved RAM space problem, but I'm out of my element here.

Here is one bug that seems similar (but not specifically related to undo).

Start with a file with wind enabled on the first element and only the first element.

Select any contiguous number of elements in the elements tab. Right click and select change sequence, and then follow.

Double click on a graphical element. Look in the wind/wave tab. See screenshot.