Die grinder runs at 25k rpms and the biggest bit that bent was 1/2in diameter, the two smaller bits that bent were 1/4in diameter. All of them had 1/4in shanks.
Maybe I will try and take the grinder back and exchange it for another one tomorrow and see if it does indeed have runout on the collet, which im assuming means its off round or not tight enough causing the burs to not spin evenly and causing them to bend.