I also have 2 passports and have swapped passports many times by air and at borders....but you can't do it at Thai borders specifically....I went last month and tried it...Cannot...!!
Yes but you can't swap them at the border while doing a border bounce as the exit stamp, cambo visa and entry stamp must be in the same passport.. Which is what this thread is about.
It is because of the volume of dodgy people perhaps....Yes I had to do one on a tourist exemption stamp last month. It is not too bad....3 hours in and out....