I noticed recently after they changed the format of their online account statements to show the pending transactions that this happens to me on almost all of my transactions on my Cap1 rewards card--but not my Platinum Cap1--not just at the pump. I've had items show as pending AND paid for several days, effectively tanking my available credit on that card. I've called each time I notice this and the CSRs I speak to always do something to minus out the pending charge immediately so my available credit is where it's supposed to be. Probably the only relatively easy conversation I have with Cap1. 
Good luck!