In the middle of a mission the other night my unit got MC’ed by a siren. 3 spider drone explosions later it was bleeding massively and I was ready to kill it at the start of my next turn, when it up and left the battlefield. I was pleased with the result until I realised that my unit was still under pandoran control with no way for me to gain it back. Fortunately it was just a mild inconvinience in that particular mission, and after some turn of shooting the structures my heavy was released from MC (I suppose, siren ran out of WP/health off the map), but in a harder mission this could’ve done some real damage to me. Seems like a bug.
Indeed seems like a bug. Did you report it?