Yea it would affect the rest of the house, it as if there is a cross connection between the hot & cold. In Delta's new packaging they send a plug to be used in one of the two ports to prevent this from taking place. The contractors either had a older packaged valve that didn't have there new plug or didn't know what it was and threw it away.
Thanks for joining into the conversation. This is definitely something that is bound to help future posters wondering what's going on.
<Spruce, making mental note: > Does anyone else smell smoke?