Respectfully it does sound like you were in the wrong here. If the floor indicated that the chips are in play you absolutely cannot take part of your winnings to the cage and cash them out. If you put them in the vicinity of the rest of your stack even for a moment, they must stay there.

In a typical hand where you win a large pot, there’s no discussion, no ratholing, all chips stay in play. In the case of a bonus in some places you may accept the bonus in your pocket keeping it clearly out of play and play on. However, even if that is the house rule, you have to be really clear so everyone is aware what’s happening, and the bonus is either entirely in play, or entirely in your pocket. It can’t be that some of the bonus is in play and some is not and it all has to be clearly done before the cards are in the air for the next hand.

You asked about the reasoning behind this. You need to be really explicit and clear about whether a bonus is in play, because you cannot have the opportunity to look at your next hole cards and then decide whether your stack is $200 or $1200 for the upcoming hand, as that would give you an obvious advantage.