Stronger taste over time

I wonder if anyone else runs into this or is there something i'm doing wrong?

Typically when I keg "lighter" beers. i.e. Cream Ale, Pale Ale, Blonde Ale, over time the taste becomes much stronger and further away from the style.
P.S. I brew extract.

After carb'ing up, the first 20-30 days on tap it tastes as it should, light suttle hints of the bitterness and grain. After that, the taste gets stronger, the bitterness increases, the beer also gets much clearer and slightly darker.
Think color going from Budweiser to Sam Adams Lager. (commercial example)

I'm not going to say its bad tasting, just different. And this only seems to happen with the kegged beer, bottles stay true.

My Dark beers this doesnt happen (or its just overpowered by all the other flavors)
Can anybody explain this?

Maybe you have some sort of bacteria in your kegs that darkens your beer and makes them more stout. J/K really I don't know how that would happen honestly. I know that time does seem to add some mouthfeel to most of my beers so that could be part of it. As far as it getting more bitter not sure on that one. Usually my first few pulls from a keg seem a little more bitter I imagine because of the sediment. Maybe the when it clears the flavor just becomes more focused so you perceive more bitterness. The color thing is maybe a little stranger.

Getting more clear is natural. But the flavors intensifying and the complexion of the beer going from a pilsner appearance to a Boston Lager....I've never heard that before.