Hi,
saving a user profile erases all joomla custom fields for that user.
I have tested this in both version 2.4.10 and 2.5.0.
Probably related to a 'bug' we are working on in Joomla core. https://github.com/joomla/joomla-cms/pull/19753
Can you please confirm / fix / help test the joomla proposed fix?