@SteveThatcher, thanks for the feedback (and I saw your issue in GitHub). We absolutely do support multiple printers in one MaterControl instance. I don't think Mike knew we had shipped the build that had that feature yet.
The build we are working on (expected to release in February) fixes the majority of these issues, but we will make sure to take a look at them again - in consideration of this bug.
FYI, I will likely break your issue up into multiple issues, link to the first, then close it.
Thanks again, we are always working to improve MatterControl and feedback is a great way to find not only what is wrong but what is important to our users.