Octave check in bass

[Christian Conkle]

I'm working on an orchestral score with lots of bassy things, and the bar and 
octave checks are keeping me sane as I shuffle notes around the score. 
However, the octave checks don't function as I expect below bass C:

\version "2.7.30"

\relative c {
   \clef bass
   c4 g=,
}

octave.ly:5:6: warning: octave check failed; expected g', found: g,
   c4
      g=,