Opening another part when one part is already open does not move the focus

[zth]

Steps to reproduce:

1. Draw two separate parts.
2. Open part 1 to the performer
3. Double-click on part 2 in the composer to open that in the performer (which is already open with part 1)

The focus of the performer does not move to the new part. My "workaround" is simply shutting down the performer and re-opening part 2 to make that focused.