gwpy-plot coherence throwing TypeError on string formatting

The following gwpy-plot call ends up with a TypeError on string formatting:

$ gwpy-plot coherence --chan 'H1:SUS-ITMY_L3_OPLEV_YAW_OUT_DQ' 'H1:GDS-CALIB_STRAIN,reduced' 'H1:SUS-ITMY_L3_OPLEV_PIT_OUT_DQ' --start 1168353018 --duration 1800 --out '/var/cache/tomcat/temp/ldvw3341239590735870542.png' --ref 'H1:GDS-CALIB_STRAIN' --secpfft '16.000'
Traceback (most recent call last):
  File "/Users/duncan/Library/Python/2.7/bin/gwpy-plot", line 118, in <module>
    result_code = prod.makePlot(args)
  File "/Users/duncan/Library/Python/2.7/lib/python/site-packages/gwpy/cli/cliproduct.py", line 773, in makePlot
    self.gen_plot(args)
  File "/Users/duncan/Library/Python/2.7/lib/python/site-packages/gwpy/cli/coherence.py", line 117, in gen_plot
    % self.timeseries[ref_idx].channel.name, \
TypeError: not enough arguments for format string

I think this is related to the way print is being used here (untested).