When the MicroFreak has MIDI Thru enabled, it only passes MIDI clock messages when the sequencer is running. This cannot be called MIDI Thru, because the device (in this case the MicroFreak) is modifying the MIDI stream.
This behaviour makes it impossible to have the MicroFreak at the beginning of chained MIDI devices as the following devices will not get a continuous clock signal.
The proper implementation would pass any MIDI message unmodified.