Recently (say maybe in the past two weeks) the behaviour of "Set your preference for birth surname display" on the Name Préférences settings page has changed, in this narrow situtation:
If one's setting is "Birth surname instead of last name", then the "Display Name" feature of profiles does not work. The name displayed for this profile will be the first name and birth surname. (For clarification, I am not talking about the name shown in the grey area, beside the profile's picture, and just above the demographic info.)
Before, say two weeks ago, and for a profile that has a "Display Name", the named displayed would be the "Display Name".
Note that for all the other choices under "Set your preference for birth surname display", the behaviour of the "Display Name" works fine.