Strange casting order

[ano]

Normally commanders in commander screen are ordered by their id - that's what I meant. So I expected that the mage with lower id will move first.
I opened the turn file under -ddd options and saw nothing special in logs. Mages were "deployed" in correct order, but the astral caster just received his turn earlier.
I wonder if this is a bug or I misunderstand something. I always thought that the order in commander screen determines the casting order in battle. How can I plan battles if it is not always so?)