At my last extension for marriage (in May) Chiangmai Immigration required me to have the Thb400000 in the bank for 3 months,. "Rules have changed" said the IO. Also, I had to produce copies of ALL the pages of my bank book, (going back over 2 years+). I was instructed to bring my bank book when returning at the end of the "under consideration" period. On doing so, the IO (a different one) handed my book back unexamined with the query"what's that for?"
I think IOs make up rules as they feel like it.