Excessive spacing due to chords

[Trond]

> I'm not top posting.

I have a problem with excessive spacing in the middle of my score. Changing the 
key from c minor to c major fixes it, even when changing to major _after_ the 
spacing issue. Is this a bug?

\version "2.12.3"
\include "english.ly"  

\score {
  <<
    \new ChordNames \chordmode {
          c1:m/ef
          c1:m/ef
    }  
    \new Staff = "right" {
          \key c \minor
          ef'''4 g''' c'''2
          % \key c \major % uncomment to fix BOTH spacings
          ef'''4 g''' c'''2
    }
  >>
}