set_ylim not working when yticks is empty

I am trying to scale the y axis like this:

a = axes(gca())
a.set_ylim((-1.25, 1.25))

This works fine when yticks is non-empty. However, if I do

a.set_yticks([])

either before or after the set_ylim call, the y axis is not scaled.

I also tried to use

a.yaxis.set_major_locator(NullLocator())

instead of calling set_yticks([]), but to no avail.

Any suggestions are appreciated.

Grig