Disk needs repaired... but it doesn't?
The apparent issues seems related to FileVault. The following steps seem to be the cure:


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).
When the decryption is done, reboot into Recovery HD.
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.
Click on “Repair Disk”.
DONE!
(Optional) Re-enable FileVault.


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