I'd have to know how you knit, as in Continental (most common), English or Combined.
I knit combined and I don't notice my stitches leaning to one side or another unless I make them do that (in decreases or increases). Also are you using circular needles or DPNs for your Round Knitting?
I have a feeling you may be experiencing laddering at the joins. If that is the case I would recommend that on the first and second stitch of each join that you tighten your yarn a bit tighter than you normally would. That's solved the problem for me.