This showed up for me first when updating from 5.0.418682.0603 to 5.1.422789.0705, and it made the interface almost unusable since you loose so much screen real estate. It bothered me enough to submit a ticket, but still no response.
There was no "autoScale" setting in my config (on Debian), but changing
scaleFactor=1 to scaleFactor=0
returned to the old scaling. Oddly after restarting zoom, this setting was overwritten and is back to 1, but the interface size is still small as it once was.
(I wish these changes were actually listed in the release notes.)