Assign votes/poll ownership not showing available users

[andyception]

While testing I also found an inconvenience with assigning votes and the ownership of a poll to users.
When inviting Users to a group it shows you the available users when you start typing the name.
However when assigning a vote to a user, or claiming ownership of a poll, it doesn't show the available users, so you need to know the exact name of the user you want to assign it to.
It would be quite nice if this feature would be available for assigning users here as well.

Also I sometimes had problems assigning Ownership of a poll to an account, however I can't trigger this bug reliably and it occours quite rarely, so I don't know what could be the cause of this and it may well be a problem with my browser.

Tested with version 0c83e17