From my perspective searching for 'casascius' on ebay.co.uk returns no results.
Does anyone else get the same?
I think that the search algorithm is just a bit complicated and you've uncovered one of its warts.
Try searching for "casascius" (with the quotes). At ebay.co.uk there are no
real hits for casascius but, without quotes, the search algorithm drops me on the results for cassius, whereas with quotes, the algorithm tries a worldwide search (giving me 22 hits). At ebay.com I have no problem.
The "0 results found for ..." message could probably be worded better.