Are there visual differences between regular and decaf coffee?
Coffee foam/bubbles is made up of a mixture of proteins, sugars, oil droplets, caffeine etc, and the lifetime of a bubble is highly dependent on the composition of its membrane. Given that decaf is coffee that's been solvent extracted, it wouldn't be at all surprising to see its different composition affecting bubble lifetime. However, no one seems to have conducted definitive studies of the matter. – answer upped from comments as requested.