I have just done the same,came back with a reentry permit,went to my imm,office with both passports,have new stamp in my new passport,they asked if i wanted to keep my old passport,kept it could come in handy if you loose your new one,,
How does one get on coming back to Thailand from Australia with a new passport but my re.entry permit and O retirement
Visa is in my old passport,
Any one have any problems
Cheers