I experienced this today. The value in Config was the updated one but the application would return the older value, stop and starting the solution did nothing.
So I cleared the .Net Temp folder.
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files
It shouldn't create bugs but to be safe close your solution down first. Clear the Temporary ASP.NET Files then load up your solution.
My issue was sorted.