Actually, I solved this problem and wanted to share. After re-routing my throttle cable and going for a test ride, it still happened! Then I had a eureka moment and realized that the same thing would happen if I were to play with the choke while idling.

So I re-routed the choke cable (and clutch cable, just for good measure). Problem solved!

When you do bar risers, you've got to re-route the choke cable. It's really simple to do and I was able to detach the cable at the choke end of things. I'm running SW-Motech risers, but I imagine the GenMars would have even more of this problem, since they come 'towards' the rider an extra 3/8ths inch over the SW-Motechs (although the Motech's rise 1.2" versus the GenMar's 1", so that puts additional strain on the choke).

P.P.S. I'm 6' and the bar risers moved the strain on my lower back farther up the back and my jacket no longer pokes into my upper thighs the way it used to. I've only ridden 80 miles on the new risers, but I like them better than stock and I'm pretty sure it's not just the luster of a new toy. I would often take my hands and rest my knuckles on the bars when coasting down hills on a long ride just to relieve some pressure. Now my hands are always in that position.

I've installed the SW-Moteh risers as well. Any pics of the choke re-route?

I had the idle speed up at full steering lock right on my 97 GS when I put the GenMar risers on almost 10 years ago, still have the same GenMars on my current 02 GS.  I just rerouted the choke cable behind the left fork leg so it doesn't pull the choke enrichers open when turned.  No problem with the clutch cable which is still routed around the front of the left fork leg.