Just to clarify, the parts aren't really surface models, they are just showing that way visually, right?
I usually check to see if a model is a surface model by going to wireframe and seeing if the wireframe shows in the color of surfaces. I actually don't know what color that is in CREO 2 (they change it too much so I set it back to the old purple color from previous versions).
Do other users in your area have the same issues with the same parts/assys? If not, I would have to guess it's your config.pro setting (not sure which one). I would then remove all the config.pro files (or rename them) and restart pro/e and see if it gives you the same display issue. IF it goes away, then it definitely is a setting. From there it gets more difficult since I don't have a clue what that setting could be so I would start systematically adding back in your config.pro files until it re-appeared. If you have multiple configs, add each one separately and see if you can determine which config it is that contains the offending option. Then systematically add the options of that config back in until it reappeared. It can be pretty challenging.
First step would be to remove all configs and see if it goes away. Pretty quick and easy test.
