Disk needs repaired... but it doesn't?

Solution 1:

The apparent issues seems related to FileVault. The following steps seem to be the cure:

1. Go to “System Preferences” – “Security and Privacy”, click on “FileVault” tab, click the lock icon on the bottom left to unlock, then click on “Turn Off FileVault”. The decryption process will take a while (hours).

2. When the decryption is done, reboot into Recovery HD.

3. Use Disk Utility to verify OS X Partition, this time the process will take much longer and it will give you the same error message.

4. Click on “Repair Disk”.

5. DONE!

6. (Optional) Re-enable FileVault.

Source: http://alanhan.net/how-to-fix-volume-bitmap-needs-minor-repair-for-orphaned-blocks-on-os-x-10-8/