Inserted parts going haywire

This seems like a bug. I wondered if others have the same problem. I created a weldment part comprising structural steel members. I then inserted various cleats and connections as parts into the weldment part. The inserted parts are mated up to the weldment using move/copy. All is well up to this point. I then rolled the feature tree back and forward. The inserted parts lose there intended position and fly off into all parts of the model like shrapnel. After trying unsuccessfully to fix this I then deleted the parts. A couple of the planes from the inserted part remains in the weldment part and I am unable to delete them from the weldment part. I'm concerned they will cause performance problems in the future.

I'm using SW 2009 SP 3.0.SolidworksWeldments