You can't put the artist and the title together unfortunately for the DiscoGS search - you have to choose one or the other and set the limiter accordingly. For example, enter "Hurry Sundown" into the search window, select DiscoGS from your list of search sites using the little magnifying glass in the search field and set the limiter in the search window to 'Title'. That should get you 9 results, the first one being the correct one.
(But I agree that there is something funky going on since not all these results match the search term so we'll take another look at the plug-in and the new API, thanks for bringing it up.)
EDIT: Conor took another look at the plug-in. One major change with 5.0.2 is that the plug-in now only picks up the 'Master' entries from DiscoGS, ensuring that the results are a bit more manageable. (When all results are returned it becomes a bit overwhelming and useless because there are lots of double entries, incomplete ones, singles, etc.) But with the cool new sub-menus that the search window offers now we've included a choice for users between Masters and Releases so if you want ALL the results for a title search, you can get them. Download
CDpedia Beta 12 for the fix.