I concur, clearing the cache is prudent.
"No, I don't see the problem on all profile pages..."
Then it is unique to that page alone (can you provide a link?). Try deleting all the birth data, save and then re-insert it.
You might also try disabling ALL add-ons, then shutting down and re-starting the browser to see if the problem may be add-on related.
If that's the case, restoring one add-on at a time to isolate the culprit would be the next step.
Another caveat (albeit a very basic one) is to insure you are running fully updated browsers.