Analogue systems

Hi all...

My Integrator has a strange behavioral quirk...it will only respond to
midi input via a midi-thru connection (not with all controllers, but
most of those I use).  

In other words, a direct midi-out to the Integrator's midi-in gets
nothing.  But if I patch the controller's midi-out into another unit,
and then send that unit's midi-thru into the Integrator's midi-in...I
get a response.

Any help would be appreciated.

thanks