ISP: Virgin Media
Type of Internet Connection: Fiber
Internet Connection Speed: 30Mbit/s
Date & Time: 6/30/2015 @ 21:09 BST
Frequency: Always
Character Name: Zeke Vardenfell
Race: Hyur Highlander Female
World: Odin
Class/Level: Dark Knight 54
Area and Coordinates: Everywhere
Party or Solo: Both
NPC Name: None
Monster Name: None
In-Game Time: Any

Steps:
1) Activate Darkside
2) Acquire a buff from another player
3) Watch as MP is drained by buff application and removal
4) HP regens will drain MP with each tick

Just chiming in I'm also seeing the MP usage when buffed form another party member in darkside. This also happens when i receive stacks of debuffs like poison.