I'm here!!

The closest thing I can compare it to from person experience is the Time Trials we do. We are clipped in and someone is holding our bikes upright so we start at zero speed. We accelerate to much faster than 22 mph...I'll have to look at some of my Motion Based dashboard stuff just to see how long it takes me.......but I'm not that fast a sprinter. I'm usually still standing above 22mph and haven't noticed any instability issues. Not sure what's going on in your case.

I even so some standing on downhills and flats for short periods to stretch on road rides at speeds that are easily above 22mph and haven't noticed an instability issues either. If it's pretty fast I might have my thighs against the frame to hold it steady if I'm not pedaling though.

Sorry can't help too much.