voiced-position malfunctions?

Hi everyone,

I was surprised to find that we now have a voiced-position property for 
rests instead of using staff-position; so far so good. Unfortunately, it 
doesn’t seem to act like it should, or am I missing anything?

Best, Simon

\version "2.27.0"
{
   \voiceTwo
   R1
   \tweak voiced-position 8
   R1
   \tweak voiced-position -8
   R1
}

%{

|voiced-position|(number):

    |4|

    The staff position of a voiced|Rest|, negative if the rest
    has|direction||DOWN|.

%}