Reply to Traktor 2.6 + VCI-100SE = Broken Sync. WTF

Hey team. In serious need of help.

Today I fired up Traktor, went to sync a track, and the synced track went all screwy. Here's the lowdown:

Loaded track in Deck A. Hit play. Deck A is master. Loaded track in Deck B. Cued Deck B. Hit sync button. Pressed play, and the track in Deck B speeds up 4-10%. Trainwreck.

What the heck is going on?

iMac with OS X 10.6.8
Traktor 2.6.whatever the latest is
Vestax VCI-100SE, v4.1 TSI

Thanks for your help!