There have been several bug reports now on the new upgrade model behavior. There were several reports on the old upgrade model behavior.
Please read this and then vote.
You can have it one of two ways:
1) Add an Upgrade Model, so 5 become 5+1. You then have to dial it down to 4+1.
2) Upgrade a Model, so 5 become 4+1. This is what the codex states.
Case 1 is how it used to work. People complained that the pricing was wrong, since they didn't notice the squad size increased.
Case 2 is how it works now and the only issue is that if you dial it up and back down, you can't bottom it out. The workaround is to remove the Upgrade model and start again.
So, which do we prefer?
Homer