Granted, my R is the first shaft drive I have owned in over 20 years (I had an '80 Suzuki GS850 way back when), but I do not remember any twist or torque from the drive shaft. I assume the twitch I feel when accelerating hard on my R is from the single side swing arm, and normal for this bike. Comments???
H-D FLHTC
BMW R1150R
KTM 400SX
"Jodido pero Contento"
As stated, it is probably the torque twist of the flat twin engine.
If high mileage, check the pivot bearings at the diff end on the drive housing, as I had worn bearings on my R1100RS I had. ( 40,000ks)
Also check tyre pressures, maybe low.