I don't know about stains, but found out the hard way, don't mix water base and oil base paints... it usually turns into jelly.
Han an occasion years ago that we pulled panel off a wall in our house and wanted to paint the room... I had two partial cans of paint both the same color and the wife okayed the color, so I mixed them and painted the room.... discovered about as I finished that one can was a water based flat nterior wall paint and the second was an oil based enamel gloss for door frames and trim work.... I had shiny streaks and flat streaks on the walls and the paint kept getting thicker and thicker as I worked... I always read the cans since then.