Another bug?: I dug up a hidden drive right outside the base which I knew was there from previous versions. It has a unique signal that I've never found by searching. When I tried to upload it to listen to it (Level 0), the signal was instead deleted. I did not hit a delete button.
Tested in Sandbox: Always gets deleted when you try and listen to it, but it can be processed as normal. Still gets deleted if you try to listen it after processing.
Also, though this may be intentional, the hidden box of level 3 signals does not give credits when sent.