I have had that experience as well, and I patiently wait for the brew to carbonate over a week or so instead of rolling and shaking.
My theory is that as the brew goes down and the aromatics have more head space to occupy, they occupy the head space instead of the brew. But that's just a theory.
Even at the bar you can tell when they're getting near the bottom of the keg. Especially if it's a specialty brew that takes a while to kick. It loses the hop character and gets more and more malty.
I suppose you could bottle the brews where you value the hoppiness, or drink it faster.
