The problem is, the rules are simple and well defined, they just don't always get followed.

Basically, the last-closed window defines the next-opened window. Except when it doesn't.

The Regedit trick didn't solve the problem, but just stumbling around I found a sort-of workaround. I always use folder view (two-pane, folders on left, files on right), and found that by moving the pane divider, shrinking the folder pane and thus expanding the file pane, I could get the window to display the information I needed in the file pane despite the overall window being the wrong size. I'll live with that until it changes again, I guess, and then try to figure out something else.

You'd think it shouldn't be all that hard for Windows to remember its window sizes...

tanstaafl.