Can't uncheck "disable extensions" in Safari Develop menu

This worked for me on Safari 11--> bottom of developer menu there is "allow unsigned extensions" click that; Now go back to the developer menu and click disable extensions...

I "fixed" it by deleting the 'Safari Extensions List' Keychain item and then restarting. I believe this is related to some Keychain issues I've been having because the Reset Password screen appeared after I restarted (after 5 mins of a black screen). After I reset my password my Safari Extensions were back but my Keychain had been blown out.

I fixed it by editing the plist for Safari to reset a variable that indicated extension were disabled after a reboot. "ExtensionsEnabled" was already set to YES -- and now that I fixed it I cannot find the key that was reset. Take a look in the plist for Safari.