Expiring passport - need advice

I have entered Thailand (Suwanna) twice in the last 6 weeks on an Australian p/p that expires on 12 April 2017. The first time was a reentry from Singapore on 11 October, the last possible day to receive a 12-month extension of stay following my earlier Non-Immi O-A visa. Duly received as 'Admitted until 10 Oct 2017'. So far so good.

Last night (22 Nov) I returned from Oz with only some 4.5 months still on the clock. The IO looked worried for a bit, then summoned a senior officer. He looked worried too. Finally they entered a stamp, then scribbled a bit, then again ... At this point, smiling & calm as always (ha ha), I asked if there was a problem. The senior guy smiled & said No problem. They then handed me back the p/p & waved me thru. When I checked it, they had first given me 'Admitted till 21/11/2017' [based presumably on yesterday's date, extended by a year - obviously wrong, though I have encountered this confusion in the past ie receiving a 1-year extension on each reentry], then corrected it to '10/10/2017' in accord with the previous extension. I think an inexperienced IO and a pleasant senior who got equally confused.

Needless to say, I am not planning to chance my luck a third time and will get a new p/p in January.