• Rez a no-copy item from your inventory into a place where you do not have rez rights
    OR
    onto most pieces of mesh (eg, not a SL prim, not the bare ground).
  • You get a message saying that you can't rez the item here.
  • The item is no longer in your inventory
The item will only be restored to you if you quit SL and restart your viewer.
So, the server knows that the item isn't going to be rezzed, the viewer knows that the item did not rez, the server knows the item is still in your inventory...and yet the viewer will not show that item until it is completely restarted.
It should be clear why this is undesirable. This behavior currently occurs in all viewers, and has done so for many, many years.