adding workspaces gives error

after adding a new workspace, the add-button gets red (with a value equal to failed) and an alert with an error message comes up: Workspace ‘portal’ already in use!
nevertheless, after clicking “ok” in the alert, the workspace exits and can be used.

(from redmine: issue id 1595, created on 2014-03-19 by Daniel.Van.Asseldonk, closed on 2014-03-30)