The system shows the user the possibility to vote for a comment or issue, although voting is disabled in the general configuration. This appears only in the activity stream of a project or user profile. If the user is viewing an issue directly, there is no option to vote.
If the user is trying to activate the vote option in the activity stream, a popup info tells "An unkown error occured while voting." (see pic). After a few seconds the info disappears, leaving the vote option unavailable.