What is going on here?(Kegging issue)

I recently upgraded from a 3 way manifold to a 6 way manifold so I can keep all 6 kegs in the fridge on gas. At the same time that I upgraded, i put two newly filled kegs of ESB in there to carb up, using the set it and forget it method. About a week later, I pulled the handle to pour a glass of Smoky nut brown ale, and it was flat. Dead flat. It had been fully carbed for over a month, and I had been happily enjoying it..., now it's flat. Wierd, I thought, but no big deal. I checked all the fittings, fully pressurized, no leaks, nothing.
I pulled the relief valve, HISSSSSSSS!!!!!!!!, let it go and heard the keg filling back up with CO2. OK.
Fast forward a week. I wanted to see if the keg of nut brown had carbed back up, so I changed the hoses around(only have 3 taps), and poured a pint. Nicely carbed, however, my beautifully colored nut brown ale is now pouring a slightly less than amber color. I tasted it, and it tastes very watered down, with no nose at all. I poured a pint from the other keg of nut brown that i had in there, and it was normal..., brown color, smoky malty nose, nice flavor. What the hell happened to the other keg?????? I have no answer for this one. Anybody have a possible answer?
Just some information, 2 of the kegs contain the nut brown ale, 2 contain the ESB, 1 contains a black IPA, and 1 contains a hefeweizen with a noticeable off flavor of buttered popcorn.
Please help.

Just a guess, but do you have check valves? If not I have heard of liquid mixing between kegs or being sucked into the regulator. Or maybe you have one or two defective valves.

are you puttimg the QD's on all the way?? shot in the dark..