KawPow confuses me

I mine with 2 cards on the 2Muner pool using trex miner. I am curious if someone could explain how the shares work. What I mean is…

I have seen many instances of a single gpu (gpu #0 for instance) submitting 2 shares in under 2 seconds. Submits one, then immediately submits another, same gpu.

Other times I can go minutes without submitting a share.

Does anyone know the logic behind this?