Probably got errataed at some point, but I never saw it. Friend of mine had two doubling seasons out. Played Pentavus. And we sat there staring at the board, trying to figure out what was the result... near as we could figure since the card didnt' say "Except counters coming from doubling seasons in play" or something it made an endless loop of counters. Pentavus triggers both doubling seasons, so that's 10 extra counters on the stack, one doubling season goes before the other just because that's the way the stack resolves, can't do simultaneous stuff, never does. So one resolves, triggers the other, the other resolves, triggers the first... Got so insane we had to house rule it and say it was just exponential, no looping, so the final result was 20/20. Checked the rules, couldn't find where it was errataed. Considering how easy it could be to get two of them out, and how many cards make counters for various things... ug.