I don't know if this is intentional but the description states you get bonus experience from ALL sources. I do quite a bit of WvW and I noticed my XP gain is the same as before.
WvW hasn't given XP in years. WXP is a separate thing. +50% of 0 XP is still 0 XP
should count for wxp its xp in that mode.
Could argue that it should have been included, can't argue that not including it is a bug as it is not among the promised bonuses . . .