Sorting by frequency/recency looks like the culprit. You often type 'for' and select forums.overclockers.co.uk, so the engine takes that into account and prior

Sorting by frequency/recency looks like the culprit. You often type 'for' and select forums.overclockers.co.uk, so the engine takes that into account and prioritizes that candidate, but you haven't done the same when typing 'forums', so it falls back on its normal sorting algorithm. Seems that if a program has frequency/recency sorting, it'd best have an additional layer of intelligence such that it checks what results would've been returned by other substrings of your search term.