I haven't encountered it myself, but I've heard of something similar when the weapon Burst= is set too high, or ROF= is too short. The infantry animation cannot play fast enough to accomodate the frequency of the weapon firing, and the unit apparently gets stuck in a loop.
that could be it. i have my GI set to a burst of like 3 or 4, and it fires very fast. Plus, it has anti air capability as well. it is the all around best unit, but until I code some good AI, it makes the AI much to easy to beat.