Maybe one of the boffins can clarify, but I think latest S/W has MAX ALT in your TCAS Loaded S/W.
Bummer if the other guy is also at MAX ALT. Maybe one gets the -2000 cue and the other gets the 0 cue.
Someone knows.
But as said, I'd certainly find a way to squeak out a few hun up if that's what the RA cue was.