Boolean masked tracks as input for best tracks tool does seem to still process all events

When I want to get the best tracks I observe that the runtime is rather high: For a random ORCA4 data file with 170k events this takes 20 minutes. Is that expected?

And when I only select a few tracks, the time is the same, indicating still all events are processed:

import km3io as ki
f = ki.OfflineReader("/sps/km3net/users/guderian/dd/datav5.40.jorcarec.aanet.00005830.root")  #a random ORCA4 file
tracks = f.events.tracks 
tracks_with_reco = tracks[f.events.n_tracks>0] 
best_tracks = ki.tools.best_jmuon(tracks_with_reco) #this takes 20 minutes for this file(!) 
a_few_best_tracks = ki.tools.best_jmuon(tracks_with_reco[:10]) #this takes as long