If the gained card is a Victory card the other players each gain a Curse. But, I replaced a platinum into a colony and the other player did not get a curse.
Game: 9345214
dullard,
You forgot to give us the game number, so I can't look it up. Was it possible that the other player used a Lighthouse on the prior turn? (Or some other "can't be attacked on your following turn" card)
I had to find the game number as I had overwritten my clipboard.
Game 9345214, no reaction cards.
Probably, the confusion is due to Expand and Replace being in the kingdom. All 3 times when a Platinum was "remodeled" into Colony it was done using Expand and not Replace. Therefore, no curses are given out. Once, a Silver was replaced into Duchy and a Curse was gained by the opponent.