When the rabbit editor starts when adding a new entity (concept, relation or instance), it is automatically filled with the correct sentence for adding the entity. However, in roo-1.0 the 'new entity' segment of the sentence was auto-selected; allowing the user to simply type the name of the new entity. This last auto-selection does not work in v1.5.0-rc1.
Fix is on the rabbit-gui git repo and will be out by the end of the week in roo-1.5-rc2.