Steps to reproduce:
1) On Facebook, click the name of a person who you share friends with but whose full profile you cannot see. An overlay will open with that person's info.
2) In the overlay, click the "n mutual friends" link. Thumbnail photos of the mutual friends will fade in.
3) At the end of the fade-in transition, the thumbnails will disappear. This is the bug.
4) Forcing a repaint makes the thumbnail appear near the left edge of the page.
5) Resizing the window, which forces a relayout, makes the thumbnails reappear where they should be.
This is reminiscent of bug 25252.
Yup, rolling out r41469 fixes this bug.
*** This bug has been marked as a duplicate of 25252 ***