Back to back commode flushing problem

We hope you can help us with this problem.

Our house was built in 1988. Our master bedroom commode backs up to the commode in the half bath.

We replaced our Kohler commode in the master bedroom with an American Standard Champion. Now, whenever you flush the AS commode it causes the Kohler commode to flush / drain in our half bath.

We have had the lines checked and the air vent...all are clear.

Our plumber suggested we move the AS commode to the guest bath, which stands alone and doesn't back up to another commode, and install a Toto Drake model in the master bathroom.

Then he called today to say he couldn't guarantee the same thing wouldn't happen even with the Drake model.

Do you have any suggestions regarding this problem?

toilets

Now, whenever you flush the AS commode it causes the Kohler commode in our half bath.

You didn't finish the sentence. It causes it to do what? Whatever happens it almost has to be a poor piping installation, not a toilet problem, per se, but a strong flushing toilet combined with an improper pipe installation could cause problems between the two toilets. And if so, ANY toilet could cause the same type of problem.

It never happened before we installed the new AS Champion commode. Is there a good commode that doesn't have the strong flush that we can install to alleviate this problem?

It's a drain/vent problem, not a toilet problem..........