It sounds like a well known TOS-problem. Especially after a program terminates the keyboard overflow with a random
character. The solution is to hold backspace untill it ends. However with accelerated STs the overflow may be faster
than reading the backspace, and a reset is needed. This has been descussed before. It happens on real STs too.
I can't remember if there ever was a patch against it; but none of clone-designers have bothered to solve it.
Cubase, (Mega)ST(e)(fm), TT, Falcon, Jaguar, MiST.