Axis labels don't appear in some instances

Solved one, now another!  Similar MWE to last time:

```
import wcsaxes
import pylab as pl
from astropy.io import fits
from astropy import wcs

fig1 = pl.figure(1)
fig1.clf()
pvhdu1 = fits.open('testhdu1.fits')[0]
pvhdu2 = fits.open('testhdu2.fits')[0]
pvhdu3 = fits.open('testhdu3.fits')[0]

ax1 = wcsaxes.WCSAxesSubplot(fig1, 3, 1, 1, wcs=wcs.WCS(pvhdu1.header))
ax2 = wcsaxes.WCSAxesSubplot(fig1, 3, 1, 2, wcs=wcs.WCS(pvhdu2.header))
ax3 = wcsaxes.WCSAxesSubplot(fig1, 3, 1, 3, wcs=wcs.WCS(pvhdu3.header))
ax1.imshow(pvhdu1.data)
ax2.imshow(pvhdu2.data)
ax3.imshow(pvhdu3.data)
fig1.add_axes(ax1)
fig1.add_axes(ax2)
fig1.add_axes(ax3)

limits = wcs.WCS(pvhdu1.header).wcs_world2pix([0,0],[35e3,80e3],0)[1]
print(limits) # should be 83, 128
ax1.set_ylim(*limits)
ax2.set_ylim(*limits)
ax3.set_ylim(*limits)

# Hide xticklabels
ax1.coords[0].ticklabels.set_visible(False)
ax2.coords[0].ticklabels.set_visible(False)

fig1.subplots_adjust(hspace=0)

ax2.coords[0].set_axislabel("Offset (degrees)")

# No dice:
ax2.coords[1].set_axislabel("Radio $V_{LSR}$ (km/s)")

# But this does?
ax3.coords[1].set_axislabel("Radio $V_{LSR}$ (km/s)")
```
The resulting figure, showing ax2 without a ylabel:

![figure_1](https://cloud.githubusercontent.com/assets/143715/4130719/6f1d5ce4-333c-11e4-9409-b12168558504.png)

And the FITS:
https://www.dropbox.com/s/2sxxd4jnv15hw00/testhdu1.fits?dl=0
https://www.dropbox.com/s/hvlom2bxtjypm96/testhdu2.fits?dl=0
https://www.dropbox.com/s/cmzxic1a1z8uosl/testhdu3.fits?dl=0

I can't reproduce this with a single subplot.