Known issue, I know, but this time I got a few save files that can reproduce the problem
here: http://share.cx.com/6ZCb79
save files:
autosave (start of mission)
2013-11-09_14.03.26.sav - v3m4 (first save after start)
2013-11-09_14.04.57.sav - v3m4a (second turn, alien stuck in rock)
2013-11-09_14.07.33.sav - v3m4aa (first turn, attempt to reproduce above - alien should end up being stuck on next turn)
If it doesn't work, try loading v3m4 and spread your troops around that rock - not too close or the alien will shoot at you instead of getting stuck, and not too far or the guy will just roam about looking for things to shoot. Just right is so he can see your guys but won't shoot due to long range, so the next thing the alien does is looking for cover, which makes the guy walk into that rock somehow.