Potential bug: Slur begins or ends with tenuto

[Daniel Rosen]

I'm sending this to the user list first because I'm having trouble with the 
search functionality in the new issue tracker, so I can't tell if this has 
already been reported:

\version "2.19.50"

\relative c' {
  \override Slur.positions = #'(-4 . -4)
  c( c)
  \override Slur.positions = #'(-4.25 . -4)
  c( c)
  \override Slur.positions = #'(-4.5 . -4)
  c( c)
}

It appears that LilyPond is refusing to allow Slur.positions to be specified in 
increments smaller than 0.5 staff spaces. I can't find any mention of a 
constraint like this in any of the manuals.

DR