I've been working with an imported model now for a over a week now.  The imported model was basically industrial design work of the outer shell, done from an outside vendor.  Then, I imported it and cleaned up any import problems, and added functional features afterwards.  Since I've been working on it, I've not had any problems, up until today.  All of the sudden, whenever I do a ctrl-Q rebuild, the top "Imported" model feature blows up, which obviously blows up all features that I have added to it, as shown below.

In the graphics area, all that is displayed are my blown up features.  The main imported body feature is gone...

When this happened, I closed without saving, and then re-opened.  Everything was fine until I did a ctrl-Q rebuild, and again it blew up.  So I closed and opened again.  I can add and edit features just fine until I do a ctrl-Q rebuild.  However, a ctrl-B rebuild does not blow it up.

I've done many ctrl-Q rebuilds over the last week or so without problems.  All of the sudden, I'm having this issue.  I will continue to work on this model with ctrl-B rebuilds only.

Have you ever seen this?  Do you know what could have caused this?  Do you know a solution to repair this?