Heroes seem to have full health before engaging in battle but once the battle mode commences

I’m playing The Dwarves for the first time and noticed something odd.

Prior to a battle one is prompted to assign the (subset of) heroes which will participate and assign artifacts from the inventory. As you can see here, this particular hero is in full health. Alas, then the battle commences my heroes start with quite a bit health less than 100%. This particular hero even has only approximately 50% health at the start of the battle (although it regenerates quickly) and the health bar shows in yellow (instead of green).

Unfortunately I failed to take a screenshot of the fact, because Flameshot (yeah, I play on Linux ?) refused to work …

I’m using easy for the difficulty level and so it seems illogical that there would be a handicap like that.

Does anyone have an idea what causes this? Is there a way to prevent it (to be able to go into battle immediately instead of having to wait for the heroes to regain full health)?