What are the differences between Visor (Deluxe) and Palm (IIIxe) with respect to serial communication?

Here's the scenario: My roommate, with his IIIxe can load up Pocketerm, put his Palm in the serial cradle, load up Hyperterm and be able to type on the computer and see the output on the Palm, and vice versa. It's working just as you'd expect.

When I try with the same software on my Visor with the serial cradle, what I type on the computer shows up on the handheld but nothing I send through the Visor appears on the PC. Why?

Would getting one of the Markspace modem instead of hotsync cables (or Handspring serial cradle) solve this problem?