Then it is not a bug.
Vitality consumption depends on exp gained.
Tried to change this?
# The following configures the XP multiplier of each vitality level. Basically, you have
# Default: 2
# Take care setting these values according to your server rates, as the can lead to huge differences!
# Example with a server rate 15x and vitality = 2. => final server rate = 30 (15x2)!
RateVitalityExpMultiplier = 2.