Issue with Slackware build of ncurses and tvi910 terminfo entry

Hello,

I discovered an issue with ncurses on Slackware, both version 6.3 used in
Slackware 15.0 and 6.6 used in Slackware-current.  I was testing a real
serial terminal - a Tandy DT-1 set to emulate a tvi910.

It turns out that, for all ncurses apps, with TERM=tvi910 I get a bunch of
spaces being printed all the time, instead of optimized cursor movement.  I
tried the same configuration on Debian 13 (trixie) as well as arch, and
these work fine.  So I started to suspect the issue is something specific
to the configure options used by Slackware.  I tested some other terminal
types, vt100 and adm3a, and they seem to be unaffected.

I have written a trivial test program here:
https://github.com/palazzol/ncurses_test
And, I think I have narrowed it down to the configure option
--enable-wmc-glitch option, which Slackware uses.  It seems like this
causes the bad behavior with this terminal type.  If I rebuild ncurses
without that, everything works fine.

Is this kind of dramatic failure expected when using that option?  I see it
is marked as "experimental".  I'm honestly not sure if my trace has
captured the root cause yet, but you can see that the test program
generates <100 bytes when working properly, or >2K bytes when not.

Thanks!