Left sidebar no longer hiding on subsequent loads

It used to be that when you load the first time and then hide the left sidebar, it would stay hidden even across subsequent loads of the page. This is no longer the case and it now always starts out open regardless of what you did before.

This started happening around the same time as I first started seeing #2299 (closed) (a couple weeks ago or so), if that helps narrow down anything.

Edit: Here's my platform version info: