Created Unassigned: Add Extender Missing after upgrade [27937]

I installed the new Ajax Control ToolKit 15.1.3.0, uninstalled an older version from an existing project and migrated the project to the new version. I replaced all the old toolscriptmanager with ScriptManager on each page. All existing controls/ extenders already on there work and the controls show up fine in the Toolbox.

I am missing all the options to extend anything new. There is no context Add Extender options available anymore.