Scorp, please upload the save file – we'll analyze it and figure everything out.

I happened to have the save file, but it's from when Khalid had already finished his turn (even though he didn't end up on the tile shown in the picture – he just kept measuring and measuring, but didn't believe why he couldn't reach it, and clicked randomly; that's not the point).
I checked: a hero with a speed of 6 would move exactly the same way as Mephala (don't pay attention to the fact that there are no dwarves now – I dismissed them after the battle).

P.S.: It's POSSIBLE that there was a bug where the speed of a slower unit wasn't taken into account; sometimes when playing as elves, Kir' would move further than she should when she was with dwarves – but I repeat, it seems that way, but here it's actually proven!!!