Changing authentication failure strategies does not work properly

STEPS TO REPRODUCE

1. Login as Admin
2. Go to Administer Wiki > Users & Rights > Authentication
3. On 'Failure Strategies' select CAPTCHA (default setting) and Save
4. Create an user (e.g. U1)
5. Logout
6. Try to login with user's name (U1) and a wrong password 3 times
7. Fill in the username and correct password
8. Fill the CAPTCHA
9. Click Log-in
10. Login as Admin
11. Go to Administer Wiki > Users & Rights > Authentication
12. On 'Failure Strategies' select 'Disable account' and Save
13. Logout
14. Try to login with user's name (U1) and a wrong password 3 times

EXPECTED RESULTS

As 'Disable account' is currently selected on 'Failure Strategies', a message is displayed informing the user that his account is disabled.

ACTUAL RESULTS

The CAPTCHA failure strategy is still displayed, although on 'Failure Strategies' is selected 'Disable account' (confirmed by logging in with Admin).

Vice versa, if the first time (before any failure strategy is triggered) is selected 'Disable account' and then after a login failure is selected 'CAPTCHA', the 'Disable account' strategy is still enforced.

It is to be mentioned also that when 'Disable account' strategy is selected and the user account is being disabled (due to multiple login failures), a 'null' is displayed above Log-in button (screenshot attached).