I would normally post this in the bug report forum, but every time i make a report and even include pretty pictures they mark it as not enough info. So just throwing this out there.

If you are on a combat class, and you meld items (since you no longer have to be in the respective class to meld) and you complete the challenge log entry "Meld your heart" it will actually grant the XP points to your combat class you are currently on.

Just got 124k XP for my BLM while melding. Just an FYI