Please verify that this has been fixed on latest 5.4.z. Thanks!
If the script generates an error, then I believe the "<script error>" is the intended outcome of the drop-down, so I don't think that is a bug. What do you mean by "reviewing the Request item"? I've tried reproducing the hang via a custom button and ordering via service catalog items. Where specifically is the hang you're seeing happening? (Might be a new bug?)
When going to Services -> Requests and clicking on the request there to view it. I am reasonably sure the Refresh button should not be there in this case.
Will create two new bugs for the things I found... Moving this to verified.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://rhn.redhat.com/errata/RHBA-2015-1511.html