So guys, funny thing. FTB sent out a mystcraft version for 1.4.1 (the 9.3.x branch of mystcraft) and somehow, it didn't cause a crash. So, http://binarymage.com/mystcraft/publish/ you will see that there is a 1.4.2 version "mystcraft-uni-1.4.2-0.9.4.00.zip". As opposed to the 9.3.X branch FTB...