Everything is in the title. I want to share that thought with you guys. Enjoy your games !
1) Priest doesn't risk a lot by RAW when taking chaos star in WFRP3. By the time of V2, they risked some God's anger (listed in Tome of Redemption). Looking at that table, I find the effect really similar to the miscasts from v3 (lost round, wounds, a demon hears your prayer...).
So that is why in my game, MISCASTS concerns the wizards' spells and the priests' blessing when there are chaos stars around.
2) we like our bits to be smart
Miscasts cards are so rarely and (mostly) briefly used that they should have been on a table only like in GM guide, aren't they ? Think about it : You take it, you read it, you give it back to the GM. That's all for miscasts, where you keep Wound/insanities/diseases/mutations/talents/careers cards in game longer (or ever).
So that is why in my game, MISCAST cards are also used to count POWERS and FAVOURS the wizards and priests gain and give back when consumed