Design issue with custom abutments inLab 4.2

Is there anyone familiar with designing custom abutments with Sirona's inLab 4.2? We are having an issue we don't seem to have a solution to, and just wondered if we're missing a step or something. We follow the steps to the letter that I learned at one of the advanced courses. Also, with the TiBase and scan body, I make sure the little ridge on the tiBase/post faces toward the buccal, and align the scan body appropriately to it. We then continue to design the case as one normally would. The issue comes after milling when somehow the little groove made in the abutment to slide down on the little ridge of the TiBase is in the wrong place and when seated results in an abutment and crown turned at least a quarter turn - even though it appears on the buccal on the screen when designing. We are baffled, and can't seem to find anyone who knows either. Any ideas?