Each fieldset on the profile page has a separate save button, but each save button reloads the page. This causes anything changed in another fieldset other than the one being saved to be lost. If all the fields are presented at once either they should save automatically one at a time without a reload (ala AJAX) or a single save operation should process all fields at once.
I understand technically how this happened and it's easy enough to work around by changing one thing at a time, but this _will_ trip people up.
Pending a major revamp of the profile page at some point in the future, we've prevented the dropping of data somewhat brutally, by simply disabling all fields except the one you are currently changing.