Changing the current project does not always mark the solution dirty

In a solution whose current Project and selected Application are different, choosing the already-selected Application from the Project selector changes the current project for the session but does not mark the solution as dirty. Save therefore remains disabled, closing Studio does not prompt, and reopening the solution restores the previous current Project.

Changing the current Project is solution-owned state and should be persisted through the normal Save workflow regardless of whether the Application selection also changes.