Thanks Tom - issue has been opened. Yes, it was the logs that gave me the filter parameters to reproduce this and isolate/reproduce this via filtering in my portlet.
This has forced me to think about this a good bit and I plan to open an enhancement request once resolved - something to the extent that, if a portlet has a filter related fail on load, fail a little more gracefully so as not to lock the user (or the administrators!) out from correcting the filter issue. Similar to the error 500 of simply running a bad filter on a working portlet.
Yes, a small issue, but this is affecting a valued user and I want to do my best for them. I'm just a little frustrated that this simple problem is outside of our out-of-the-box administrative toolset to resolve.
When I get this resolved I'll post up my results for future
Knowledge.