It might be a Mono issue and I would certainly welcome any help in diagnosing and reporting Mono bugs to the Mono team. With enough help it is possible that things will get much better on Mono and I will feel better about recommending it.
However, I'm not sure, it might also be a problem to have a space in the labelResourceKey, I would try removing the space and see if it changes anything.
The expected result is for it to show the property on the Profile Tab under My Account and also on the manage user page that admins can get to from the member list. It should also appear on the ProfileView.aspx page if the user viewing the page is authenticated.