Blind transfers to FXS ports disconnected

FreePBX, Asterisk 1.4.17-1, Aastra 480i phones w/ firmware.

I have several 480i CT phones at a location that also includes several cordless analog phones connected to a Sangoma FXS (zaptel) card.

When performing a blind transfer from the 480i phones to any of the analog phones, (Xfer button > ext#) the caller is are disconnected as soon as the person transferring hangs up. Attended transfers to the FXS ports work fine.

Any ideas? Transfers (blind and attended) work fine to the IP phones, and to an ATA.