To the best of my knowledge, yes, still a problem. The immigration officer will expect you to have a tm6 in your passport. The action he takes will depend on his mood at the time, and his interpretation of the rules. You may be taken from the queue and into a side office to be processed. That's the best I can tell you, remember Thai immigration officers are police officers, don't argue with them.
you must find this tm6 card, if you still have it. Thai Immigration are very strict about this document being kept with your passport. I lost one a year ago and had to pay 300 baht for a replacement at Korat immigration office.
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