When in combat and learning evasion if I cast PHP I will stop learning evasion.
Evasion 215
fighting maidens tress (220 cap?)
cast php at 25 mana
Avshara
I've also noticed it while using other "buff" spells but not notably so (IVM, OBF, etc).
It seems like the xp calcs are using the buffed rank/stat to use rather than the base/actual skill rank to figure xp given. This is in both test and plat side.