Redmine

• Create a Role "Project Update"
• do not provide permission to "create project" or "create sub projects"
• Provide him "Edit Project" permission
• associate a user with this role to a project having a parent project.
• Login as a user and edit the project.
• Modify the description and save.
• The save fails.

Environment:
Redmine version 3.1.1.stable
Ruby version 2.2.1-p85 (2015-02-26) [x86_64-linux]
Rails version 4.2.4
Environment production
Database adapter Mysql2
We are using 3.1.1, But may exists in other versions as well.

Attaching the patch for the correction.