Bug report

Bug summary

Code for reproduction

from pylab import *
rcdefaults()
imshow([[10000, 20000]], norm=matplotlib.colors.LogNorm())
colorbar()

Actual outcome

Expected outcome

Either both tick labels use a superscript exponent (preferable), or neither does.
Noted while investigating #12473 (comment).

Matplotlib version

• Matplotlib version: master, present as far back as 2.0.0.