2,4D resistant Palmer pigweed

I have a field that roundup resistant Palmer pigweed showed up in last year. I wasn't going to plant beans in this field this year because of the Palmer so I decided to plant pearl millet for hay as a double crop after small grain. There was Palmer that came up after I harvested the small grain so for a burn down I sprayed a mix of roundup and 1.5 pints of 2,4d figuring the 2,4d would take care of the Palmer. It make it sick for about 10 days but then to my surprise it snapped out of it and started growing vigorously. It was only 3-4 inches tall when I sprayed and I can't see any reason why the 2,4d would not have worked. Has anyone else seen Palmer that is becoming resistant or tolerant to 2,4d?

2,4D resistant Palmer pigweed