This sounds like an AC problem, but it doesn't happen in 2018 on Panther. It seems to happen only for libraries loaded from servers.
If you use the Finder to open a library part that is in a currently loaded library, when you save the part you will be warned that it has the same name as a part in the loaded libraries, as if you had opened the part from a non-loaded library.
The saved part gets filed under "Other Objects" in Library Manager, and if you don't delete it from there, you will get a duplicate report on reloading. Note the duplicate doesn't actually exist; the paths of the dupes are exactly the same. The old version of the part is still cached and will be favored, so placed instances will act as if the part had not been edited, until you delete the "Other" item and reload.
Opening parts by selecting them in AC works as it should, which is fine except for macros and templates.
