Issue using PortMidi on Mac OSX Intel, 64-bit

I'm seeing an issue regarding Pm_Initialize failing on Mac OSX on x64 
architecture.  I have a MIDI USB device powered on and I can send it data 
successfully, but if I don't send it data for a few minutes (5 or so), when I 
try to send it data again the Pm_Initialize call fails in MIDICreateClient.  I 
get a return code of -50 (paramErr).  I issue Pm_Terminate every time and it 
initially works when I start my application.  The call to Pm_Initialize seems to 
fail only if I wait and don't send any data for a few minutes.  This same code 
works fine on Windows.  Is this a configuration issue on Mac, or a coding issue? 

Help, pointers, etc. are appreciated. 

Dan