Today we've switched over to a new gazetteer, the directory on places which is used when you use the search box to go to a location by name. Previously we were using the Ordnance Survey's OpenData gazetteer but of course that was restricted to places in Great Britain so you couldn't search for places in Ireland such as Dublin or Belfast.
So now we're using the Nominatim search engine from OpenStreetMap and you will find all searches are done using that the next time you re-load the mapping application in your browser.
We've tested this ourselves using all our favourite searches but there may still be things that need tweaking so please let us know if it doesn't find things you expect, or indeed you get matches you wouldn't expect (initially for example we were getting matches on some post boxes!). Either post here or contact us directly. A screen shot would also help if relevant.