It's always worth a complaint, but I couldn't even work out the story with the $600 thing. We missed the $600 for Mitchell AND the $3000 too.

It should be pointed out more clearly - when you ring thro earnings, it doesn't actually have any bearing on the income estimate you give for FTB. It is competley separate.
If you are classed as current I would take that to mean you are currently eligible, but that you will rec FTB at the end of the year. Also that, once both your tax returns are in at the end of the fin yr, the ATO will automatically transfer your income info to C'Link and will generate yr payment without a claim hving to be put in. If you are paid based on actual income, there will be no overpayment.

You can get some FTB thro the year and the rest in a lump sum if you like. Like I said, it is worth putting in a complaint as that means that someone will have to go right thro the issue again, and the mistake could be picked up. This does take a bit of time, although it shouldn't.