I know this is a bit dated, but I ran into this tonight. Same symptoms. Works without Mobi51, does not with. My working theory is that Request.Browser.IsMobileDevice is touched by Mobi51 and it takes control of that property and sets its value regardless of what you would expect .NET to do with it.
My current solution is this. When I check in my viewstart file to switch layouts I check that both Request.Browser.IsMobileDevice and Context.GetOverridenBrowser().IsMobileDevice are true.
When it's truly Mobile, both will be true. When it's truly desktop, both are false. When it's a mobile view requesting desktop, Request.Browser.IsMobileDevice will be true (because Mobi51 says so) and Context.GetOverridenBrowser().IsMobileDevice will be false. Here's my viewstart
@{
Layout = Request.Browser.IsMobileDevice && Context.GetOverriddenBrowser().IsMobileDevice
? "~/Views/Shared/_LayoutMobile.cshtml"
: "~/Views/Shared/_Layout.cshtml";
}
I'm still vetting this and have to add desktop to mobile switching still (which I can already see a problem, but the change to make that direction work as well is easy enough , but in my five minutes of testing so far tonight this has worked. I'm curious if you found another reason/way to work with this, or if this solution is satisfactory for you.