Thanks for pointing out the inconsistency with the version number in the original post...got that fixed (the post said 5.1, but download is 5.2) :)
I'm super interested in what you find out...the only way I could reproduce this is by attacking one target (or no target) and dragging damage to a different target. But this behavior is consistent with a brand new campaign with no extensions loaded at all.
Let me know what you find out and if it's not that, I'll certainly get on it ASAP.
Thanks!