If you are affected by the login bug where the keyboard doesn't show when entering credentials, Samsung have released a fix.
This bug was actually a bug introduced by Samsung itself in their fall firmware update.
This is the firmware version you need if you're affected by the login bug:
R830XXU1BTA1/R8300XA1BTA1/
Tizen ver 4.0.0.7
The fix is verified by many customers already and the app is now functioning as intended.