As Thestpaul kindly points out Xenophobia, you should not lose your tag during the fight when you are MC'd and once the fight is over, you should be able to claim loot. :)

It would seem that the petition you put in for this matter Fenrix was done a month ago when we were investigating into issues with interacting with this boss.

Please try it again now and if you are still having difficulties, you are welcome to raise an in-game petition where it will be looked into further.