I also use a number of library parts created in AC 6.5.
Perhaps superstitiously, I have, at the desktop, duplicated each part,
put the duplicates into a new folder, opened each one in AC 8.1, corrected
any parameter settings that are wrong (line types, fill types, etc.)
and saved.
This updates the parts and gives them the subtype data and obligatory
parameters of a native 8.1 library part.
In AC 9.0, just to be "safe", I go through the same process.
This may be nonsense but it might cause some file updating
that fixes problems with objects created in earlier versions.
Thank you,
Peter Devlin