If you right-click the cluster...advanced...customize to go to the control editor, resizing is possible. If you then exit the control editor, replace the original control, and don't save, the cluster is again resizable in the VI. Something must have been corrupted, and this seems to fix it. (LabVIEW 2014).
Thank you Knight of NI.
It works in LV8.2.1 too.
I'm glad you didn't sent me into the shrubbery to cut it down with a herring