Was this a proper call?

Situation: 12U all star district tournament game, loser's season is over.

My son pitching, first inning. One on one out. Batter hits a slicing fly ball to right field. It curves foul by a few feet, very close to the wall.

Home ump calls it foul. )I was sitting directly behind home plate in the press box. It was a good call. We also have it on video, showing the ball clearly foul. Not that this matters for what happened next.)

The base ump, who was behind second base on the play, called time out, called the home ump over, chatted with him for a few minutes, and the home ump changed the call to a home run.

I was the official scorekeeper for the game, so the home ump had to explain to me why he changed the call. I argued that he made the call, and it was his call to make since he had the down the line view. I said that the base ump can't make that call, unless the home ump needs his help and asks for it.

Was I right? It may not be a rule, but isn't the base ump supposed to simply support the call?

The interesting thing about this situation is that the base ump has a history of ill feeling toward our league. He's a longtime ump in a rival league, and one time openly laughed about ringing up one of our players in the All Star tournament on a neck high fastball.

The person who heard him say it filed a formal complaint, and he was disciplined by the district. That was the year before.

I've seen a lot of bad calls in my time, but this is the first time I ever saw what I would characterize as intentional malfeasance by an ump.

Am I right that he had no business even opening his mouth on the play?