You are jumping to a random conclusion that the metadata in the original file is messed up. That conclusion is unwarranted by the facts at your command.
At no point did I state that all filenames are truncated. I did however state that
calibre can and will do so, when it deems fit.
I do not care to guess when and how that will trigger, and I will CERTAINLY not try guessing when I have not been told what actual path was used... unless your crystal ball came online and you can tell me the exact path that the OP didn't mention to us?
There are few people who have read the manual more than I have.
P.S. calibre will rename the in-library file whenever you change the metadata. If it left the files wherever they were first added to, that would be in effect violating (to a small extent) Kovid's ironclad rule as laid down in the sticky+FAQ.