Update.

Ernie Gilman reached out to me on this. I want to amend my statement to say that the Pronto must be the first discovered device and that gaps don't always cause issues.

Consider that you have a mouse on COM1 and the Pronto on COM2. The software sometimes misidentifies the mouse and fails. If you switch them around such that mouse is on COM2 and Pronto is on COM1, it will work fine.