Gary:
I had that happen a few times over the years, while guiding clients and actively in the field. Kind of a pain-in-the-neck to deal with when it's either freezing or blowing or precipitating outside, like there's no tomorrow, But, remedying the MSR stove situation is rather easy. Just replace the O-ring(s) in the check-valve. It's a pretty simple fix, actually. Be sure to clean and dry everything before you put it all back together.
Mav
