I had similar situation few months back. I went to few DMVs, and finally went to Carrollton, TX. Initially they didn't want to issue DL even with STEM extended OPT I-20 (which is until dec 2012) and Notice of Action from DHS. But they talked to their supervisor and they let me in (they issued me a ticket number to get in line). Again when I went inside, the lady refused, and called her supervisor. The supervisor told that request I-20 won't work and it should be approved. Then she looked at my STEM OPT I-20 request end date and I have no idea what happened to her, she approved it.
I went to 4 DMVs over the 2 whole days, and what I learnt was you need to have 6+ months of "approved stay " (not requested) in US in order to get DL in TX. I just got lucky.