"Group instances of the same type do not contain identical members.... etc."

We have all seen this when copying groups. What I would like to know is how to avoid this when grouping unit plans in multi-unit residential projects.

For the most part they copy seamlessly and there are no issues. But our client wanted to add a curtain wall partition, so I added it in and clicked "finish group" and the stupid prompt appears telling me to "fix groups...".
Is there a way to embed the curtain wall system separately or attach it like a detail group? Or do I create a window family that looks like a curtain wall and use it to avoid this.

Best practices here?

Thanks