I don't believe the filtering is particularly effective. google.co.uk has gotten worse over time, with many listings showing businesses that do not sell to the UK. It's pointless displaying them in the SERPs when specifically choosing UK only.
It may not be connected, however, personalised search does not help, so give the cookies a good clearout.
Also, searching for a term which is not an English language word will tend to bring in 'most relevant' terms, which, might be the issue in this example.