Special:UpdateProfile looks similar to Special:Preferences where the information is presented in several tabs/sections. However, when you navigate between sections, one would expect (unless otherwise stated) the information to remain "in memory" until you save the changes. However, navigating to other section actually is navigating to another page and the information you entered, unless saved, is lost.
It would be good to at least watch if the user did a change after saving, and pop up a warning when the user wants to navigate to other sections that the current modifications will be lost unless saved.
This is a minor UX issue.