FWIW, I've attached screenshots from my setup (not emacs -Q),
from Emacs 23.4 (which is the same as Emacs 22), Emacs 24.3,
and Emacs 24.4.

It is Emacs 24.4 that manifests the bug of this report (but
the bug is not shown in the screenshot).

You can see that already in 24.3 the black lines separating
the windows are doubly thick.

In Emacs 24.4, there is the added glitch that there is an extra
blue line in the brightness window (rightmost window).

All three screenshots show the non-bug condition of the frame.
I present them just to show that things have changed in Emacs.

I can live with the changed behavior (though I don't understand
it - in particular, the thin blue line).  I can try to debug
that separately.  But I thought it might help to show what
happens when this bug does not manifest itself, as well as to
show some of what has changed in Emacs.  The code is the same,
and is pretty straightforward.