I think the problem is when the temperatures get below a certain point, the carb starts to ice up. I notice on my four cycle engines that the intake manifold develops a lot of condensation on it when i fly in the morning when it is chilly. if it was near freezing temperatures, the condensation would turn to ice on the intake manifold.
Plus below a certain temperature the nitro/methanol/oil mixture begins to separate.   I think I remember reading about a guy in Northern Canada and when the temps went below -30 degrees F, was when his fuel would get funky on him.