Cigar tar in clipped area.

Had this happen a couple of times this winter on two different brands. Everything is going along nicely when suddenly the taste in my mouth turns rancid. I check my smoke and notice some little bubbles of a tar-like substance at the clipped end. First time I took my cutter and clipped a little more of the cap off and it seemed to save the smoke. The second time I couldn't save it. Is this just an over-oily leaf or some other reason?

I've never had this happen before. How 'bout you?