Celestial meridian labels incorrect for eck4 projection

I am testing the following eck4 meridian labeling example:

def label_bug(celestial=True, lon_0=65):
    m = Basemap(projection='eck4', lon_0=lon_0, resolution=None, celestial=celestial)
    m.drawmeridians([lon_0, lon_0 + 60], labels=[0,0,1,0], labelstyle='+/-')
    m.drawmapboundary()

With normal coordinates, the labels appear where I expect them:

label_bug(celestial=False)

When celestial is True, the meridians are correctly flipped, but the labels no longer match their positions:

label_bug(celestial=True)

If anyone knows a workaround until this is fixed, please let me know. Thanks!

Start with the supplied label_bug reproduction and Basemap.drawmeridians, comparing celestial=False and celestial=True for the eck4 projection. Trace how meridian positions and labels are transformed, then verify that labels match their displayed meridians in both cases using the example.