I confirmed this on v5.0 (but I noticed it on v4.3).
Joomla is 2.5
I have a FB Connected user:
- if I login using username + password, the SCLogin button shows the "connect button", ignoring the fact my user is allready connected (it shows up on the User Map backend)
- if I login using the FB Login button, no "connect" button shows
Hope it helps to improve