Not sure why I didn't do this earlier ... /bonk.

I launched my main WoW instance, and then only two alts. I did the same types of tests. Type out sentences, do various slash commands, etc. I got the same missed key strokes here and there. EG: "/dance" gave me "/ance" on both alts. (No sign of that really weird "a,n,p,u" issue I described above as of yet.)

Well that eliminates system resource taxing as an issue. Now the only other variables I can see are dual-monitor with two graphics cards and the version change of keyclone from S to U.