I think the new gas blends are more volatile than in the past. Modern cars have the pump in the tank and the whole fuel line is highly pressurized (~40 psi?), which would tend to reduce the boiling. Our cars have neg pressure on the suction side of the pump and then only about 6-8 psi between the pump and carb. I noticed the same thing in my clear filter and, like Bjorn, solved it by removing the glass filter and adding a filter next to the tank. But I'm sure the fuel is still boiling in the fuel line and carb but my car runs OK. I figure while the car is running, the fuel pump just keeps pumping gas into the fuel bowls to keep them filled with liquid gas and the excess fuel vapor just gets burned. After the car sits hot, like you said, it may take some cranking to get enough fuel back into the carb.