Kerbal Space Program

when I hit the undo button sequence (command-z on osx) in the vab or sph, I tend to get more undoing than just one step. occasionally, it will delete my entire vehicle, but sometimes it will just go back a couple of steps. after this first undo, i have also noticed that the game will undo even if i do not press the z button and only press the command button, however, if i then press the z button (without pressing command) it will no longer undo if i press command, and then require the sequence command-z again. this works both with and without mods, and is not new to ksp .21.1

possibly unrelated: I hear the system alert sound when i hit command-z

i speculate that the game is not registering the release of the z button after command z is pressed, and/or that the undo function is being run once per frame while command-z is pressed, and not just being run once.

specs: macbook pro (mid 2009)
ksp .21.1 with and without mods
osx 10.7.5
2.26 ghz core 2 duo
8gb system ram
NVIDIA GeForce 9400M 256 MB