Workspace and Project Shared Views on the Portfolio Page do not keep the Release filter value when changing between different projects.
That’s working as expected. There isn't a way to determine if the release is in the project you change to, therefore the filter value is removed. Furthermore, releases and iterations have unique identifiers for each project therefore even though the Release name is the same it will not be the same Release in different projects.
This is the View which was created for the project showing up in the Project Scope :
As you can see the Release value is kept.
And this is the situation where the same View has been chosen in a different project :
The view hasn't been actually chosen and the Release value has been removed.
In order to use the same view (with the same filters/columns setup/etc.) under a different project, you will need to create a new view for each project and once such view is created it’s easy to modify and re-save:
As you can see it's a different project and now the Release retains the value correctly since the separate view has been created for this very project.