It may be the way it's meant to work, but "Microfighters" only brings up the first series & micro fighters only brings up a ninjago make & take build. I figured that since Brickset BrickLink & BrickOwl treat it as a Star Wars sub-theme (since all four series so far have been Star Wars) it would be better to bring it in line with that here.
I am afraid, though, that the fix introduced one small bug (or I didn't notice it before). The estimator widget for lost parts says something like:
Estimated value: X (Based on Y% of the parts)
When drillling e.g. into a specific category the Y value is way larger than 100 which seems little bit strange :-)
Also can you consider showing total parts count instead of unique count in brackets after each drill down field? This seems to me as a more logical number upon first glance.