My employer overpaid into my 401k account (ie: deposited an extra paycheck's worth of money into the account). I notified the HR/payroll person of the mistake, and they said they'd "look into it", but no action has been taken.
With the end of the year approaching, thus tax reporting time in the US, I'm concerned about what my liability might be for the extra deposits amounts over what was withheld from my paycheck. Since it's a 401k, I can't just return the money.
Note: my employer does not have a matching or profit sharing program, so it wasn't a planned employer contribution.
Update: I started work at this employer during 2012, so there isn't the possibility of a 2011 contribution being deposited in 2012 calendar year.
The amount is equal to one paycheck's withholding, so 9% of 1/24th annual salary. So not a huge amount, but enough to stick out.