Cannot enable back a user after it has been disabled for being spammer

A user detected as spammer is automatically disabled. However if this is false positive we need to be able to enable back the users with the UI button on the profile.
Apparently, this UI button is not working in that case.
Reproduction step:

• AntiSpam disable a user
• Go to this user profile, there's a green button "Enable this account"
• Click on the button

Expected result:

• the user is enabled back

Obtained result:

• the button is immediately switched to "Disable this account", but if you reload you can see that the user account is still disabled and the button is back to "Enable this account". The history shows the last change as "Disabling user considered as spammer".

Workaround: enabling back the account, works when going in the object editor and changing the active status.