Ok, so my coworker was trying to make an extrude off of another planar surface by offsetting the whole sketch (a rectrangle with fillet corners) by 0.0001". The preview shows what you would expect (a shelf of .0001"), but when the model rebuils, SW decided to just merge it into one! So, really there is a tiny taper, like a loft. Very weird! Is there a setting for this "tolerance" of the model itself? I tried cranking the line/model quality all the way up (the tessalation, as it were), but it has no bearing on this. It's like the program is a making a decision to "blend" the stepped surface into a ramp.