I had this problem and was also baffled until I spoke with Doug Dutra, the famous slant six guru. He explained what was happening:

When you shut off a warm engine, the heat from your engine's intake manifold is boiling the fuel in your float bowl and causing it to drip into the intake etc causing an excessively rich condition. This happens because the fuel percolation drops the float and allows more fuel from the still presurized fuel line, between the fuel pump and the needle and seat to flow more fuel into the carb to bring the float level back to normal. This continues until the pressure in the fuel line between the fuel pump and the needle and seat goes to zero. In the mean while, a significant amount of fuel has now percolated out of the carb AND the pressurized fuel line between the fuel pump and the carb (until the presure is released by the process). Quite a bit of gas ends up in the intake every time you shut off a hot motor.

This is how you fix it:

#1 Use two gaskets and a sheet of aluminum to isolate the carb from the intake manifold. This will likely require longer carb studs. Be sure to check for hood clearance. (this helped a lot, but did not eliminate the problem completely)

#2 Install a fuel return line from a 3-nipple fuel filter, which is available from any autoparts store between the fuel pump and the carb, and the fuel tank. The third nipple on the 3-nipple fuel filters has a metered orifice to limit the amount of fuel it flows. I had to install a return line and a 2 fitting fuel sending unit on my 68 slant six car to complete this installation. The car had an original 5/16 fuel line, so I added a 3/8ths line as the main fuel line and used the 5/16ths line as the return. I bought a dual fitting fuel sending unit for less than $50 off ebay, ran the lines, installed the 3-nipple filter. I never had a hot start problem again.