An update for anyone who is following this thread. After doing some debugging on the side, it appears that the patch is working with the 2.4.1 codebase. We're not sure why it wasn't working before; the best guess is probably something to do with odd caching by the mod_perl side of the apache server.
Gavin
WeBWorK Main Forum
Limiting responses with a .def file in 2.4.1
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