Sending clips from FCP to Soundtrack Pro shortens clips. Help!

I'm editing a video of nearly two hours. When I send an entire audio track to Soundtrack Pro it bogs the computer down badly, so I tried breaking it up into shorter clips and sending just the referenced media. That works fine for the first clip in each track. I can remove noise, etc, and it makes the round trip back to FCP.

The problem comes when I try to send a second clip from the same track. It dramatically shortens the clip before sending it to STP (see image).

I've tried setting different in and out handles, skipping several clips and doing one further down the timeline (that just gives me an error message: "General Error"). Here are the settings I've been using when sending from FCP:

Does anyone have any suggestions? I would GREATLY appreciate any help you could provide.

Thanks!