How to revert an override in partcombine

[Ed Gordijn]

Hi,

I use an override in partcombine to ignore collisions. But how do I 
revert this again?
In the snippet below I trie to revert but this doens't have effect and 
the g in the last measure collides.

I know that \once does work but I would prefer the construction with 
\override and \revert because I want to use this in longer sequences too.

Greetings, Ed


\version "2.18.0"

musicI =  \relative g' {
  g1~
  g1
  c2 c
  g1
}

musicII =  \relative g' {
  % create a double tie with partcombine
  \partcombineApart
    \override Voice.NoteColumn.ignore-collision =##t
    g1~
    g1
    \revert Voice.NoteColumn.ignore-collision
    % tried both revert and override but there is no difference
    % \override Voice.NoteColumn.ignore-collision =##f
  \partcombineAutomatic
  g2 g
  \partcombineApart
    %\override Voice.NoteColumn.ignore-collision =##f % works, but why 
do I need it twice
    g2 e
  \partcombineAutomatic
}


\partcombine \musicI \musicII