Try to manually edit the "Installed Packages" (right click the Task, select "reset", now you can edit the section)
and change it to :
-e git+ssh@github.com:user/private_package.git@57f382f51d124299788544b3e7afa11c4cba2d1f#egg=private_package(assuming " pip install -e mailto:git+ssh@github.com :user/... " will work, should solve the issue )