You can create another Note from the same lemma:
This is working as intended. There's no particular reason why it would not be valid to have multiple notes attached to a single lemma.
Hmmm. I thought the user would do that outside of the Notes tool. I notice this can be done for text datatypes, but here the new note/highlight is for the reference, overwriting the original text that was selected in the resource.
Just seems unnecessary to offer Notes/Highlights in the tool.