Hi shayne, see here for a description of where you need to pick on each surface to control the placement and rotation from one surface to the other:
http://moi3d.com/forum/index.php?webtag=MOI&msg=5853.2

You may be doing something like clicking right at the corner point where it becomes ambiguous which side you are actually aligning with. You don't want to pick directly on the corner, you want to be a little ways inwards from it so that there is one distinct edge that your pick is closest to.

- Michael