You (and everybody else!) should always check the stamps in your passport. Mostly it isn't on purpose but because they (immigration) really work as fast as they can.
Do you have a reliable Thai friend or person to go with you? Do you have several branch offices of these banks? It often comes down to the attitude of the branch manager.
Where did you do it? Some places like Pattaya have a very bad reputation, as the Immigration wants you to proceed with the help of an agent, so they can make some extra commission...