Had this in Kanachanaburi a few years ago. They were roaming around the bridge area, one of the main tourist spots, and surrounding tourists and demanding to see their papers. They did it to us, I was with a friend from the UK, after she basically said "What the hell was that bs?"
It really is not a good look. They played the good cop / bad cop routine, with some of them being friendly while some were aggressive in their questions. When I showed them my stamps on my phone, one started questioning me about which counter I have to go to get the extension. Plus, all decked out in military style garb.