and I knew what a mess it would be.
During my staying with the same employer, my salary changed from time to time, due to different withholding,
1) no any withholding at all (except parking)
2) any withholding but FICA
3) all withholding
Since tax treaty is only applied to federal tax, I believe I needed to pay all tax/ins but FICA, although employer may have made a mistake.