I had the same thing happen on my last double knit project, where I was holding the yarn in a new way, and the awkwardness somehow translated into stitches where half the V was big and loopy!
I believe it is indeed a tension problem. I'm not certain, but it seems like it's just a matter of getting a firmer hold on the yarn. If you wrap the yarn around your pinky as I show in the basic knitting video, you can shut the pinky against the ring finger to keep the yarn from coming through.
KnittingHelp Queen Bee
It is not because things are so difficult that we do not dare; it is because we do not dare that they are difficult.