Power stance makes attacks cost 1 extra AP. Using a weapon above your level costs extra AP. Various debuffs can cause a lack of AP. Heavy armor increases the cost of movement. Just some thoughts.
Did you read my post?
Yes. I think you're overlooking something.
Okay, I'll humor you.
I am looking at my character screen now...Madora does not know Power Stance, so that can't be it. She is level 7 with a level 7 Scythe (req: 4AP), so that can't be it. The last time this happened the first thing I assumed was that she was under some neg effect (which I've seen increase AP cost in the past, I'm aware of this), but she was totally healthy. She's wearing a Light Mail Armour type which actually gives her +0.1 movement, and she has 2 points in Armour Specialist, so I wouldn't assume this to be the issue either.
The weirdest thing about this is that it has happened during times when I have two back-to-back attacks queued up in the same turn...the first attack costs 4, the second attack costs 5. That makes it really hard to figure out what's happening...perhaps it's a bug?