Have to say that from my point of view on transition/conversion means exactly that - an IAS or Mach to fly when transitioning from one speed schedule to the next. If I was given 250 knots on transition in the descent then I would never have assumed a problem with maintaining a higher speed until the transition, and likewise if I was give 320 knots on transition in the descent I would not see a problem with keeping a slower equivalent mach until transitioning.
Surely if you folk in ATC say "speed 250 knots on transition" and what you actually want/require is 250 knots know then you should say "reduce speed 250 knots"?
eckhard, can you give a reference for on conversion implying an acceleration? I am not assuming you are incorrect but without a reference that isn't what the instruction implies to me nor any of my colleagues I have recently asked.