savefig.transparent has no effect when saving from UI

Bug summary

The savefig.transparent rcparam does not affect figures saved from the GUI.

Code for reproduction

from pylab import *
rcParams["savefig.transparent"] = True
plot()
show()

then click on the save button to save a figure.

Actual outcome

The figure has opaque background.

Expected outcome

The figure should have transparent background, just as it has when calling savefig().

Matplotlib version

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