This one has me stumped as I do the same process of all imported files.
I have an imported assembly that has hundreds of small parts all of which have density set to 1.0E-10. The part has a weight of 1.72e-09 lbs and the assembly (only part in the assembly) has a weight of 17.2 lbs. Changing the density doesn't seem to drive the assembly weight anymore. All units are the same and I have every peice in the assembly checked out. changing the densities always yields the same result.
Any ideas what might be causing this?