Maximum Menu Width won't change

I have the plug-in installed with the twenty-eleven theme, works great, however when I change the “Maximum Menu Width” and save it in the settings it always reverts back to 960. I get the message that the changes have been saved. But for some reason it’s not sticking. When I go back into the settings it is once again set to 960.

https://www.ads-software.com/extend/plugins/responsive-select-menu/