The following illustrates a slight inconsistency in matplotlib:
a = subplot(111)
Since the default linear minor locator is NullLocator, there are no
minor ticks to use as a template when the default logarithmic minor
locator is used. This results in the minor ticks being drawn on the
right as well as left axes. It seems more logical to add a flag
somewhere indicating that tick_left was specified, and check this flag
when configuring ticks from scratch. Likewise for the xaxis.