Thanks for posting that question!! My DP and I just inseminated this last weekend and the same thing happend. Spermies in the butt crack!!

We were using fresh sperm with a 1cc needless syringe. I took a poll on another website and 60% percent said that happens to them as well! So I guess it must be natural. We even tried leaving the syringe in for 20min, but some still decided to make it's way aroung the syringe ( I hope they were that determined to make it into my cervix!).
Good luck to you!!