[RevSmoke]

Dont think it is unusual. In fact, expect it! It is why I take a couple solid pulls on my pipe before lighting. Sometimes it is there, sometimes not. I do agree that it might have to do with the type of tobacco cut is packed. I also think it is a greater probability that it has to do with the humidity level of your tobacco. If you are smoking drier tobaccos, it is possible that a bit will get into the draft hole and cause this problem.

Peace of the Lord be with you.