That was my experience too few years ago in an Amphur tax office in Chiang Mai when asking my taxes on fixed deposits back.
They said never seen this before and, since i was on retired visa they didn't believe i was not working. But at the end i got the reimbursement. Same thing the next few years.
This year just did it two days ago and all was much easier with no hassles and fast, some new personnel working there probably with more knowledge, and about my incomes they just asked if i had anything to declare, which was none. Only they said i will have to wait about 30 to 60 days to receive the check because foreigners are done for last.