~snip
When you try to tweet the referral link a different message displays:
~snip
But when you try to fix it at your profile description a message appears saying it's considered malware:
~snip
I've used shorturl.at. Right after posting it works perfectly, but when I checked again few minutes later destination was removed already and the short link redirected to the main official shortener page.
Did you encounter that in the web version? If so, their android application does not have or display such a message. After I tweet a direct referral link, it just notifies 'failed to send tweet' and when I put it on the website (edit profile), it prompts 'profile update failed'.
Pastepeso.com is what I use, it will let you create and publish plain text containing links. It works and is not detected by Twitter as Freebitco.in referral link.