re: "undoing" roth contribution and "redoing" it in the same year.
my suspicion is confirmed that yes, you can do this. if you do this, you'll get a 5498 showing you contributed $10k to a roth IRA for the current tax year (these are mailed out in May, keep these as it is the best way to prove what your basis is). You will also get a 1099 from the managing institution showing the "undo." These are mailed out usually by the end of Jan. The net of the 5498 and the 1099 should be $5000 or less for 2012. You MUST call the managing organization and explain you made a mistake and want your contribution for the year back. They need to code the 1099R correctly so the IRS doesn't doesn't blow an o-ring. You'll have to pay tax + 10% penalty on any EARNINGS. This is done on form 5329 I believe.
At this point, it is as if the contribution never happened. So, you are free to contribute again by 4/15 of the following year.
Assuming you can get the institution to code the 1099 correctly, this is much more straight forward than a first time home buyer's distribution. pub 590, pg 62 under the title, "are distributions taxable?"
Withdrawals of contributions by due date. If you withdraw contributions (including any net earnings on the contributions) by the due date of your return for the year in which you made the contribution, the contributions are treated as if you never made them. If you have an extension of time to file your return, you can withdraw the contributions and earnings by the extended due date. The withdrawal of contributions is tax free, but you must include the earnings on the contributions in income for the year in which you made the contributions.