Oh shhhhh***ttttt I think I found a large gaping hole in the rules.
I hope I am wrong soot holes in this PLEEEZE. :)

5th level Mage (not wizard) casts Rope Trick.
5th level Mage (not wizard) climbs Rope, leaves Aerbynnis space and
enters an "extradimensional space". He studies all the spells he
could not learn in Cerilla, among them Fireball for example.
5th level Mage (not wizard) can now memorize Fireball by entering an
extradimensional space via Rope Trick. He can't recover the spell until
he re-enters another Rope Tick but that cost is small compared to the
power gained. (IMHO)

The Cat is now out of the bag. :(

Proposed solutions;

1) Rope Trick is forbidden or does not work.
2) Rope Trick opens into Shadow World and makes a lot of noise
doing so.
3) Something else.

Ideas ?