Closing a project should release all resources of the project file
 
I am working on cleaning projects.
 
I open a project, do some stuff (bounce to clips), save and close. I then attempt to delete the old bounced-from files, but am informed the file is open in Sonar.
 
This is not a good idea. All files/resources, not essential to Sonar's existence, should be released with project close. NOT requiring a Sonar close.

I would also do a PR on this.  This is the kind of thing I think is silly to have to do a FR to get corrected.