I finally registered for a Twitter account and just added it to my Daniweb Profile.
At first, I tried to add the full URL, but an error message popped up stating only letters, numbers, and underscores were allowed. So I changed the field entry to my username only (not even the @ sign.) It was then accepted.
In the Google Plus field, the complete URL is entered, and is behaving as expected.
In the LinkedIn field, the complete URL is entered, and I believe it is behaving as it should.
It seems inconsistent that some fields accept the complete URL but another refuses to.
Is that how it is supposed to work?