Hello arymetore and welcome to the forum,
Sorry it appears that no-one has noticed your post. The regular members don't log in as much as they used to unfortunately. So I will do my best.
I don't have experience with Emerald sabers I just have regular Obsidians but perhaps the problem is the recharge port causing the strange switching of funtionality. I recall a long time ago that some owners wanted the ability to have their sabers plugged in continuously so as to use the saber as a decoration on their walls and I think Ultrasabers changed the way the Recharge Ports were wired up. You mention both sound and light work but at different times so maybe the RC is the problem (being located between the LED and soundboard/Emerald).
Other than that I can't offer any other possible reason so if you haven't already then maybe send Customer Services a quick email to enquire for help. Send them a detailed explanation of the saber and setup you have and describe the problem as clearly as you can (if possible send a video too). Hopefully they will troubleshoot your issue and advise you of your options to rectify the problem or see about getting repairs booked.
Sorry again for my lack of Emerald experience and the slightly late response.
Please let us know how you get on if you do contact Customer Services. And I hope you get your saber back working as soon as possible.
The email address for Customer Service/Info is
[email protected]For Tyeth.