diagonal joining line

When I am crocheting in rounds (to make a hat, for instance), why do my stitches "travel" to the right with each completed round forming a diagonal line? I don't have this problem with double crochet, but it always happens with sc and hdc. Am I "joining with slip stitch" to the wrong place?

Forums: 

If you are increasing each row at the ending of each row this happens SO > try the increase evenly around.
I also make my joins on every other row from> the back to the front < >instead of front the front to back !
Or sometimes every 2nd row .

I have shared this idea with many ladies and they like the results.