This may be a bit long. However, it most likely will be relevant. I purchased a brand new Super Tenere last week. I found from day one that often I could not change down gears. Changing up was fine. Always seemed to happen when I was coming up to an intersection, roundabout etc. I was very concerned about being rear ended because of a stall.
After reading numerous posts on the forum I dismantled and lubed the gear shifter at the pivot point. The lubing didn't make a difference to my problem.
After a lot of riding and being able to replicate the problem quite often I stumbled on a process to prevent it from happening. I found that if I lightly pressed up the gear shifter after changing down a gear the problem would not occur. So now I could ride the bike safely. Now bear with me I will eventually get to the good bit.
I rang my dealer (in Goulburn 100 km away) and discussed the problem with him and he advised to bring the bike in so that he could check. One of the mechanics rode the bike around town and advised that he could not replicate the problem. He asked another to take the bike for a run. As soon as he returned he adjusted the gear lever so that the part of the lever that you move with your toe was lowered (about 5mm). I then took the bike for a test run and now it changes gear as one would expect.
So it appears that I was not moving my size 12EEE foot far away from the gear change lever to allow it to return to the rest position when frequently changing gears when coming up to intersections etc. Lowering the tip of the gear change lever fixed the problem.
Anyway, a big shout out for Chris Weekes Motorcycles in Goulburn for caring about my problem and coming up with a solution.
Hope my experience may be of use to someone