After further investigation I do not believe this is a defect, If you turn off the thematic display option (which is set to slope) in the display style that is used, it will turn off the MS slope value at top.
The top Value is coming from the calculated value MSTN gets to perform the Thematic Display. If you try height …it would appear height instead of slope. This values takes account more than just the Terrain Model but all microStation graphics…so they can be different.