There is (or at least used to be) an option on your iPhone that forces the messages to be sent and received over SMS rather than iMessage. I wonder if one could turn on that option on their old phone before switching numbers.
There was a fairly recent change in how iMessages are handled. In one of the iOS updates, you can receive iMessage messages on numerous devices tied to your Apple ID such as your iPad. I wonder if that's where the bug comes from.
The other option is to switch to Android at home and get new friends.
I wonder if one could turn on that option on their old phone before switching numbers.
Yes, one can, and this is the correct and documented way to avoid this problem. Unfortunately, people don't generally think about it before asking their carrier to swap out phones on their line, and your iPhone has no way of knowing you intend to deactivate it.
There was a fairly recent change in how iMessages are handled. In one of the iOS updates, you can receive iMessage messages on numerous devices tied to your Apple ID such as your iPad. I wonder if that's where the bug comes from.
The other option is to switch to Android at home and get new friends.