Can't delete subfolders of symlinks in a subst-ed folder

That sounds like the Recycle Bin is displaying that, as it's not something Opus itself would display.

My guess is that you're deleting to the Recycle Bin in Opus and Explorer but not in the other programs you tested, which would explain the difference between programs.

What the Recycle Bin does is more or less down to Windows. Opus can bypass the Recycle Bin if you wish, but then obviously the files can't be undeleted (or at least not as easily).