But only when you're walking around. When you're fighting the round ends when your AP are depleted or too low to do anything.
There is however a mechanism that when you're leaving the map and go to a new map, the round counting resets and a new round starts.
The same reset mechanism seems to work when you start a fight. Not a big deal you would think, but it is!
It is the most obvious in the conditions that cure or drop your hitpoints: you can walk for more than a minute without being weakened by poisons, as long as you leave a map or start a fight within 5 seconds (that fight must be won in your turn). And that "within 5 seconds" isn't very hard to do, its harder to do nothing in this game for 6 seconds.
I thought I should share this observation with you all. I wouldn't say the round reset mechanism is a bug, it's just how the game works. But like all undocumented features, it's good to know and be aware of!
This way, I made alive it to Thorins bed once, with lethal Irdegh poisons in my hero's body

But there is a downside as well: it makes regeneration and even shadow regeneration a lot less useful, because they're not quite as often triggered as you would think...