any monsters u kill if u are in a group u will get a (Group Bonus) EXP on any mob. This is based on 3 things.
1 If u are in an instance the max level is voided.
2 How many people are in the group max exp at 5 members.
(A common thought is that if a high level runs u in an instance u dont get full exp. Lvl 80 running WC. This is not true the problem lies in most power levels consist of one high level and one low level thus u wont get the full group bonus, just fill the party to 5 and u will get full exp

)
3 Outside of instances the max exp awarded is based off of the highest level in the group, so keep the levels close!
Hope this helps its no glitch what i just stated its the game mechanics