Checkboxes only appear when you are initially posting the listing.

When you go to change the location, the user interface presents you with radio
boxes.

You've got two choices:

1. Delete the original listing and recreate it, this time with the appropriate
locations.

2. Create an additional listing that looks identical to the first listing and
link it to the appropriate locations.

When the listing is created, you can place that listing in more than one location  in the taxonomy. What is really happening, if you choose multiple locations, is that multiple, individual listings  are being created.

After that, you can only move one listing at a time because each listing is an individual listing, not the same listing with pointers in each location.