Foam- First glass good, the rest are not

I've read lots of foam posts here, most start with 'first glass is foamy, the rest are ok'. I have the opposite problem.

Little background, I just put my keg setup together a week ago. Beer is fermenting, so I put rootbeer on tap (dedicated keg for pregnant wife). Tried it with short line, didn't work, got longer lines, ~35' of 3/16" with a cobra tap. Force carbed at ~35, served at 35.

At the first pour, the line is solid root beer, and pours pretty well. But after the 'stagnant' root beer in the line empties, I get lots of foam. When I stop the pour, there's a ton of bubbles in the line. If I let it sit for awhile (overnight), the bubbles disappear and I get that first good glass again.

Any idea what's going on here? Would a leaky dip tube o-ring cause that problem? Maybe excess CO2 is leaking into the line when I try to pour, and while it sits overnight the CO2 bubbles in theline dissolve back into the root beer? Or is it the other way around, for some reason CO2 is coming out of solution when I pour? But if that's the case, how does it fix itself while resting in the line?

CO2 always comes out of solution when you pour...that's why you get foam. I think you have yourself an overcarbed beer(root). That's why I avoid the 30+psi method. If you never set your pressure above 15psi, you'll never have an overcarbed beer.