It wasn't a mistake on your part. The issue is that JMRI only has the info that's available in the decoder to identify it, and the Soundtraxx decoders in the first run of RTR SD40's (announced in July of 2014) identified as Bachmann Sound Value decoders.
The correct JMRI decoder entry for those early RTR SD40's is the SD40 listed under the Genesis models. Not sure why it's listed there since it's an RTR model, but I do know it's the correct one (I had a small part in helping to creating it).
As an aside, the newer RTR SD40-2's correctly identify as Econami ECO-200's.
I got a new Athearn SD40 DCC / Sound loco. I put it on the JMRI program track and loaded into the roster and made my changes. I put it on the layout and ran fine except the front and rear headlights were blinking. At first I thought it might be roadname specific because it was a logging roadname. I talked to a friend and was told they should not be blinking. I put it on the program track about 6 times changing lighting cv's and nothing worked. So, finally I put back on the program track and when I opened JMRI and and selected that loco, I noticed at the bottom of the page it showed "Bachmann Sound Value Decoder" installed. I deleted it from the roster and re-programmed it as an Athearn SD40 and yes, it worked fine. Haste makes Waste as my mom always said.