Windows 8.1 64 bit, 8 Gm RAM, Intel(R) Core(TM) I7-4500 CPU1.80 GHz 2.40GHz GPU: AMD Radeon R7 M265, Intel(R) HD Graphics Family. Version game 1.40f11
War for the Overworld Launcher Log.txt
I can't reproduce it either. My first guess was that the vampire simply was too far away from the prison so that, once he'd go for dinner by the time his blood need was at ~50%, he would be at 0% and thus angry once he would actually reach the prison. However, it appears that Vampires can actually teleport to the prison at will (which may be a bug in itself, I'm currently testing it in the internal build).
Maybe try to give the Vampire gold or drop him in your Vault. Possibly the problem is connected to the bug where minions stop working in their designated rooms because the did not recieve their payment. Hope it works as workaround.
The gold on this map, I had always in abundance, any unit could receive his salary. I gave the vampire a thousand gold (with the appropriate spell) is useless, the vampire is hungry and unhappy. I threw the vampire next to the prison - he ate one prisoner, but was left hungry.
You try to reproduce the problem on your supercomputer, and similar to my laptop. Most likely, a vampire is hungry, when the game eats almost all free RAM.
I throw a vampire near the prison. He eats the prisoner. But still hungry. In the end, he rebels.