Hum... odd.

After knitting a couple of projects with ribbing, I've noticed a little something odd. Everytime I go from a knit to a purl, there seems to be a lot of extra yarn and it results in unsightly holes in the fabric. But going from a purl to a knit is fine, nice and tight, no gapping holes. I wonder if it's just me and I need to learn how to knit properly, or if it's something that is "normal". If any of you knitting guru's out there have any advice, I'd really appreciate it!