Udar Clan Thief XP comparison to Udar Clan Thug XP

What this problem is related to? (e.g. Game / Launcher / Website / etc. ):
Monster Stats

Describe the problem:
They are comparable in level and power but the thieves give lower xp than the thugs, they should be quite similar with the stronger one giving a bit more.

What was the expected behavior?:
average around same xp rate

Screenshots/Videos (if available):
Level 17 Udar Clan Thief

Level 17 Udar Clan Thug