Can't format former Boot Camp partition
So I stupidly erased my Boot Camp partition using Disk Utility rather than in the Boot Camp Assistant. And now I the partition is stuck as free space and i can't change it. When i select the free space in Disk Util, I can change it to Mac OS Extended and ExFAT as usual, but when I press apply, the progress bar appears for a brief second and disappears. Then it acts as if I never pressed apply; when I close the window, it says that I have unsaved changes. The free space does not appear as a drive in the left sidebar.
I have tried reinstalling OS X, I've tried returning to a time machine backup, I've verified and repaired the disk, but nothing has worked.
I'm left with 67GB of space unusable on my macbook now.
MacBook Pro with Retina display, OS X Mavericks (10.9.4)