This happened twice in a row in two different games where my gf's hero had extremely low HP, something like 43 HP. This happened to me too in the first game that it happened to her. I chose the same hero as I usually do too. The second time it happened it only happened to her.
Another thing about it is, the HP value of each point of STR she had wasn't scaling the way it should. She had like +221 STR with only 1700 HP =/.