After upgraded to the newly lanuched (2 days) version 6.x-1.4, the CK Editor disappears sometimes. Firebug caught the below error:
uncaught exception: [CKEDITOR.resourceManager.load] Resource name "tableresize" was not found at "/sites/all/modules/ckeditor/ckeditor/plugins/tableresize/plugin.js?t=B5GJ5GG".
I put the CKEditor files to sites/all/libraries/ckeditor and specifed in the CKEditor module setting page that the path should be "%l" << the library path. However from the error above it seems that the module still try to get the CKEditor files from the folder within the module. After I copy another copy of the files to the folder inside the module, the CKEditor appears again.