Why can't I \override TieColumn #'tie-configuration only \once?

[Urs Liska]

Hi list,

I know that I can tweak the ties in a chord to my liking by overriding #'tie-configuration like in the following (intentionally useless) example:

\relative c' {
  %\once
  \override TieColumn #'tie-configuration =
    #'( ( 8 . -1)
        ( 3 . 1 )
        ( -3 . 1)
      )
      <c e g>2~ q |
      <d f a>~ q
}

This doesn't really make sense musically but works as I expect it to.
But if I uncomment the second line and add the \once clause I'd expect that only the first tie (c major) is engraved according to my TieColumn. But it seems that instead no manual changes are applied at all, both ties are printed "normal". The override doesn't take place at all when preceded by \once.

Is this expected behavior, am I missing something?
Or should this be considered a bug?

Best
Urs