Hi Robert,
I am using the standard Vitamix container, it is huge, and it has small vents, so … no I don’t have that problem. There are smaller single serving containers for the machine that work just as you describe and they are not recommended for blending hot items.
I just like my coffee hot. For years, I have been preheating my cup in the microwave so that the cup does not cool down my coffee. After blending my coffee with cold butter and room temperature coconut oil, it is just not at my preferred temperature so I just microwave it for 30 seconds.