Sorry for hijacking a Turkish part of the forum, but a couple of friends ask me for a fair opinion about that.
Well, the MP bonus is not bugged at all. From a casual 30 mins PK with a full MP set (255 + 162 MP), Mage AP SC and top items (FR Book 11 + one Akara +3 FR), I was able to reach:
2265 by Meteor Fall
1528 by staff
2944 by Igzination
I have no time to build a fancy vid so a screenshot should do:
Any way to reach such DMG, an opponent has to have a low Flame Resist.
Also, you have to remember that will full MP set on, you are becoming a glass canon, so full-time draki blessing is a must.
I hope it helps.
Have a good evening !