Failure due to the amount of Larkwell pickaxe mining in the workshop

I noticed during an exotic mining mission that the amount of exotics mined with the Larkwell pickaxe was unusually low. I completed a mission with 64 basic exotic rewards and only 52 were rewarded. I have not checked against the amount of mining for other minerals, but the amount of mining is probably less than the stone pickaxe, not just +133% of the amount of mining in the performance (16 with the INARIS pickaxe and only 13 with the Larkwell pickaxe) The finest pickaxe in the workshop is performing less than a stone pickaxe...