If it's showing up in your "convert experience" window, it's on the tank, and will be possible to use to research to next tank.
If you keep "accelerate crew training" on - you will NOT get any experience on the tank itself. It will ALL go to the crew.
Remove the checkmark in "accelerate crew training" - or you will never get any experience on the tank to research/convert. It's as simple as that.
The only "bug" preventing you from accumulating experience right now, is the fact that you have accelerate crew training turned ON. Needs to be OFF.
It's going straight to your crew right now, since you have accelerate crew training turned ON.