Spells disappearing from spellbook - could be related to EnablePvpRules()

Description:

Every artifact weapon spell (like http://www.wowhead.com/spell=205545/odyns-fury , http://www.wowhead.com/spell=205495/stormkeeper) randomly disappears (not always) from spellbook after accepting a duel or going into a PVP area - at least from my tests these are the only cases where the spells disappears.

I suspect it has something to do with EnablePvpRules() as I commented this from code where duel start happens, and spells does not seem to disappear anymore.

Current behaviour:

Accept a duel or go into a PVP area (like Gurubashi Arena) - your main artifact spell disappears from spellbook (it is not unlearned), it gets greyed out from action bars if you have it there and can't cast it anymore unless you relog (then it appears back).

Expected behaviour:

These spells shot not disappear at all.

Steps to reproduce the problem:

As above, through duels or going to PVP areas.

Branch(es):

master

TC rev. hash/commit: rev. 2d666810d2ce

TrinityCore rev. 2d666810d2ce 2018-04-28 16:36:42 +0300 (master branch) (Win64, Release, Static) (worldserver-daemon)

Operating system: Windows Server 2012 R2 x64

Start by tracing EnablePvpRules() through the duel-start and PvP-area handling described in the issue, then reproduce with an artifact weapon spell such as Odyn's Fury or Stormkeeper. Compare behavior with that call enabled and disabled; done means the spell remains in the spellbook and castable after accepting a duel or entering a PvP area without requiring a relog.