We, too, are having this problem, even when exporting to GEOPAK TIN. It is very frustrating to perform all sorts of edits to a terrain, only to find out that when exported, the edits are not there. The terrain is exported since other downstream processes can't quite yet use terrains and must use GEOPAK TINs or InRoads DTMs.
Feel free to read through the following thread. communities.bentley.com/.../282639.aspx.