Trinitycore: [3.3.5] Warsong Gulch exploit: Flag with mount

[Raydor]

Description: Warsong flags are able to pick while mounted if done correctly. If you click the flag in the last millisecond of the mount cast bar, you can mount and then pick the flag, resulting in you being able to carry the flag while mounted. Here is a video that shows this behavour (it's hard to reproduce, just give it some tries :P):
https://gfycat.com/DefensiveElderlyCapybara

Current behaviour: Players are able to carry Warsong Gulch flags while mounted.

Expected behaviour: Players shouldn't be able to carry Warsong Gulch flags while mounted.

Steps to reproduce the problem:

1. Put the flag in an open area where the player can mount and then go near the flag (at the pickup range)
2. Cast any mount spell that is not instant
3. In almost the last millisecond of finishing the mount's cast, click the flag
4. You can now move mounted while carrying the flag

Branch(es): 3.3.5

TC rev. hash/commit: https://github.com/TrinityCore/TrinityCore/commit/0048d4b618e6503a5f1607f3503fcf2d48e6a385

TDB version: TDB 3.3.5 63

[Raydor]

@Keader Nvm it works, im retarded (forgot the "new spell_warsong_flags();")

[Treeston]

Core bug - AURA_INTERRUPT_FLAG_MOUNT is checked in Unit::Mount, but listed steps add the aura _after_ player is already mounted. Aura should check interrupt flags on apply (and remove if matched).

[Killyana]

I don't know if it's related or not but druids could keep the flying mode if they use the fly form when the character touch the water, in this case the player can fly (without fly form) but also can cast spells, it's not easy to reproduce, it took me 5 min.

[Duratans]

I would like to add, this bug is still existent in latest revisions, as OP described.