I finally found the post that had FixIt instructions here; Yosemite Recovery Update 1.0 bug
. That fixed it
That's a pretty old thread and for a different purpose.
So here are updated instructions more relevant for just updating the recovery partition to a 10.10.4 version. It's almost the same, but more modernised for public releases instead of developer previews:
1. Download the Lion Recovery Update from https://support.apple.com/kb/dl1464?locale=en_US
. (And before you ask, YES. I mean LION recovery update!) Make sure it is in your downloads folder. If you still happen to have the full yosemite installer somewhere, right click on the Install OS X Yosemite.app file and click Show Package Contents. Go to Contents/SharedSupport/. Copy the InstallESD.dmg file into your Downloads folder. If you don't still have the full installer, you can get it again by redownloading from your purchases tab in your mac app store.
2. Download and decompress the file recovery.sh.zip from http://4unitmaths.com/recovery.sh.zip
and move recovery.sh into your Downloads folder if it's not there already.
3. Open Terminal and type the following commands:
chmod +x ~/Downloads/recovery.sh
4. Wait a few minutes for it to finish and return back to a prompt. Reboot with holding down the option key to test your recovery partition.
(Although if you have core storage you will have to revert it to make the recovery partition show up in the startup manager. Just run these in terminal to revert it if you want to:
diskutil cs list
diskutil coreStorage revert lvUUID
where lvUUID is the last lvUUID reported by the previous Terminal command. Then restart.)