Acids taste sour (as opposed to bases, which taste bitter). Pineapples do not taste sour. Fresh pineapples contain bromelain, which is corrosive, but this is denatured with heat and cooked pineapple dies not have the sharpness that fresh pineapple does.
I cannot relate to any of your statements about cooked pineapple taste because I have never experienced it as you describe.