Weird thing

[4_cell_racer]

Raced the X-Pro on friday night at my local club, I have upgraded the rear pin holders to the alloy ones as I thought it would be a fit n forget part plus it would make it stronger!
Well I was wrong, as I tapped the barrier at fairly low speed and out pops the rear arm As far as I can tell there is no damage to the pin holders (only the inserts) and the pins still look straight

Has anyone else had this happen??
Also where can I buy the inserts from?