Strange Clematis Issue

I have what I believe to be a Jackmanii Clematis. The first flowers that bloomed had 6 sepals. Then the other day I noticed a few with just 4 sepals. Now I am finding them with 5 sepals. They are all on the very same vine. Other than that they look the same in every way. The color is the same on each flower. It doesnt look like any of the sepals are falling off. They are just growing that way. Is this just typical of a Jackmanii or is there something else going on here?

Mine does that, too. I don't know why, but it happens every year.

I think I remember reading somewhere that Jackmanii does this.