Saving a file with save-as does not update the filename in the buffer
tab or the mode-line.  If you switch buffers to any other buffer, then
switch back, everything is updated.
I reported this behavior about a year ago in 21.4.24, but that was a
frozen code base. After installing 21.5.29 (without any subsequent
patches) on a Windows XP system, I noticed the problem was still there.

I took a screen shot of it, right after a save as and am sending it
along. You can see the windows title bar has the new name. but the mode
line and the buffer tab have the old name.