Is that Mono 4.0.0 or .NET 4.0?

Mono. I think it's a bug or something.

    Mono JIT compiler version 4.0.0 (master/c198a39 Pk feb 21 22:02:35 EET 2014)
    Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
        TLS:           __thread
        SIGSEGV:       altstack
        Notifications: epoll
        Architecture:  x86
        Disabled:      none
        Misc:          softdebug 
        LLVM:          supported, not enabled.
        GC:            sgen

I JUST (today) build from source on github and got this:

     mono -V
    Mono JIT compiler version 3.4.0 (master/8f2d3ea Wed Feb 26 11:59:41 EST 2014)
    Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
        TLS:           __thread
        SIGSEGV:       altstack
        Notifications: epoll
        Architecture:  amd64
        Disabled:      none
        Misc:          softdebug
        LLVM:          supported, not enabled.
        GC:            sgen