4.0.8: Can't turn Designers Mode off

[ehren.]

I've upgraded to 4.0.8 and temporarily enabled Designers Mode (in an attempt to fix bugs from earlier versions).

I'm now trying to disable Designers Mode, and it's stuck in an endless loading page. I have tried multiple times with the same result.

This is on a live site, which won't cope well with DM enabled since it's resource intensive.

Any help is appreciated, thanks..

 

 

Edit: Ticket #918590 has admin details if required by developers