lol, poor Rexxar.
In the RoC human campaign level 2 (where Uther defends the base and Arthas kills the blademaster/Searinox), I encountered a really strange bug. When the blademaster illusion comes over to your base, it starts a cinematic. However, Uther was still attacking a grunt when the cinematic started. After the cinematic was over, the grunt ran back to his base all the way at the top of the map, and
Uther followed. Uther proceeded to wreck their entire base & all their units for the rest of the map. I didn't even have to worry about protecting my base. xD Divine shield is OP.
I also had a really weird technique of completing the last level of RoC on hard mode (Hyjal). At the end (where Archimonde comes in with all his cronies), I pretty much lost all my units and everything except the night elf base with still > 3 or 4 minutes to go. I just had furion and a bunch of wisps/mercenaries. I went and built a side base, and fortunately they attacked that first (it was out of the way, so it bought me some time). And then I kept making treants with force of nature, and I would lead Archimonde and all the baddies away from the base just to stall. This only worked until the last minute, and then Archimonde came and started wrecking everything. With 5 seconds left, he was just a feet steps away from the circle of power. I summoned some treants nearby and they got in the way of his path, so he had to walk around them--and it barely bought me enough time to complete the level. He literally was on the circle of power by the time the clock hit 0:00, I was shocked and so relieved it counted as complete.

That wasn't really a bug, but it was an enjoyable/intense experience.
Good times.