ASP.NET state server not working with 32-bit web gardens in IIS10

It appears that the out-of-process session state feature in IIS only works for 64-bit web gardens, but once the "enable 32-bit applications" flag is turned on in the application pool it reverts to InProc session state. I won't get into the reasons here why I need both of those features, but I have managed to make a simple test application which seems to prove this is broken in IIS10 where it worked in Server 2012 / IIS8