If you enter the Outerlands from Thaumcraft the Mana Mirror isn't able to drain mana from its bound pool. Whereas when I enter the nether it is working fine, thus the pool must be loaded. Is it a bug or a feature (from thaumcraft) ?

Edit: using the lates botania r1.4-157 with the latest Thaumcraft 1.7.10-4.2.3.4.

The pool naturally needs to be loaded. Whether TC unloads stuff or not I wouldn't know.