what the heck are my Communion Slaves doing?

[Zooko]

General fatigue question:

Why did my Magus go from fatigue 0 to fatigue 45 after casting Body Ethereal. I double-checked and there were no extra fatigue effects such as "excessive heat". His encumbrance was listed as "6", and his spellcasting encumbrance was listed as "6". Body Ethereal is listed as costing "20-" fatigue. It is an A1 spell and my Magus has A1.

This is kind of irritating. If there is some reason why he gets extra fatigue then the game should tell me what it is!

P.S. I'm irritated because I scripts my Magi to do Body Ethereal, Luck, Body Ethereal, Communion Slave. However because the spells inexplicably cost twice as much fatigue as expected, they tired out and didn't cast Communion Slave, thus screwing up my tactic.