Is the NCD X terminal character reversal really an NCD problem?

[dmitchell@APCTRC.trc.amoco.com (Donald H. Mitchell)]

In December on SLUG, we had a discussion about the merits and drawbacks of
using X terminals as Symbolics consoles.  I had mentioned that we are
currently doing that with our UX (sun embedded symbolics) boards and NCD color
X terminals.  I had also said that we have this gnawing problem of the
characters reversing color:  i.e., if you set the foreground to black, then
very often the characters come out white when you scroll or bring up pop up
windows.

Someone (whose note I'm too lazy to look up) wrote that they not only have the
same problem but convinced NCD that it was an NCD problem.  While a member of
my staff is trying to find out what they can from NCD about this conviction,
I want to ask why it happens in the way it does.  In particular,

WHY DOES IT ONLY HAPPEN IN LISP LISTENERS AND EDITORS?  Not in the document
examiner or our own applications or other such things (unless they have editor
windows)?  Why do mouse clicks (even on the scroll bar) seem to start the
problem?  Could it be something at least non-standard about Symbolic's X?
(I'm desparate for a solution.)