Is it acceptable to overstay my TR visa while waiting for a decision on my Non-O visa application based on marriage?

I have already applied at Surin Immigration to convert my TR visa to a Non-O visa based on marriage to a Thai national, and I am now awaiting the outcome. I was told I would hear from them by March 12th, but was advised to call ahead in advance to confirm beforehand. I called immigration today and was told no decision had yet been made and that I may not hear from them until after my TR visa has expired on March 15th. I was told that overstaying due to these circumstances wouldn't be a problem. This doesn't sound right to me at all - am I wrong?

I have a receipt from Surin immigration for the payment of Non-O visa application, but they did not stamp 'under consideration' in my passport, or indeed any stamp at all.

Any advice appreciated.