Profire 2626 Recording into pro tools with no output on record enabled track

[finkbmx]

Hello, I am having an issue that I think may be a bug or something. I have a Profire 2626 and M Powered 8 on a Dual 2.7 G5 with 8gb ram running leopard. I am recording a vocal and using the onboard dsp to have no latency in the cue mix. Now i created sessions and set them up so that I could record my vocal along with a guitar track. These tracks that I made allowed me to record enable them while having no output assigned. I thought great now I wont be double monitoring, and I can still have my sends to reverb and such without sending them pre fader or muting tracks. This was fine until i wanted to record a harmony, so I duplicated the vocal track without the regions and set it up to do the same, but now when i hit record enable i get a message saying pro tools cannot record enable track because it does not have active inputs and outputs. I don't understand how a duplicate track can not work when the exact same setup on another track works fine. I hope someone can help me figure this out. I know there are plenty of work arounds but I want to know why its doing this. Thanks, Dave