The job of identifying a chord from the notes being played is too complex for a full analysis always to be practicable.

The program has to sort out, identify and ignore passing notes, overlaps and other quirks. It all comes down to deciding which notes are part of a chord and which are not.

The program does not give an instantaneous snapshot of each separate collecion of notes, but attempts to take an average over the specified beat.

Incidentally, you can specify how many chords per bar, so in 4/4 time, you could have one, two or four. The averaging will takeplace over a different period, so the results may be different.

E.g. you may just play a G chord for the whole of a bar, or it may be a G and a C, each over two beats.

Where there are two possible names for the same 'chord', i.e. set of notes, (like Em7 or G6) depending on the inversion, the program does attempt to take into account the key signature. However, given that stating the key is optional in MIDI files, this is sometimes just a guess.

Hope this helps