Dear Aunt TUAW,
Hi, I found (the hard way) what seems to be a bug in Lion's new "Versions" feature. If I take an image that is on the desktop, make an edit (e.g. annotate it) and then quit Preview, it automatically saves the change.
Then if I open the file again, I can use File->Revert to Saved, and restore the original, all fine. However, when the image is on my USB memory stick, it is all good until I try to restore the original version. It says "No previous version available" and "Time Machine can't find your backup disk."
This is obviously a huge problem. If I make edits to an image on the USB stick, I need to manually undo everything before quitting to prevent them from being saved. Is this an issue on your computers as well, or is it just me?
Your loving nephew,
Versions does not work on non-HFS+ volumes. It's likely the format of your flash drive causing these issues.
Normally, Lion saves your app versions in .DocumentRevisions-V100 in the hard drive root, but only on HFS+. When you edit a file on an unsupported volume, Lion deletes temporary versions when you close the document. That's why you're seeing that behavior. There are no versions to recover to when you work outside of HFS+.
You can easily reformat your thumb drive to HFS+ in Disk Utility. Follow the directions in this post for partitioning and formatting the stick. Once reformatted, Lion will be able to create the revisions folder, and allow Preview to access those earlier versions.
Another advantage for HFS+ formatting is this: when you use HFS+ you can also use FileVault on your USB sticks, which will prevent anyone from being able to read its contents if it's lost/stolen.
Auntie has added a few extra versioning notes for the interested (read "geeks") below this response.
The Document Interaction Control Menu
Here are a few tips about versioning that you might not have known about. You've already seen the document interaction menu, the triangle-based drop-down menu that appears to the right of the file name in the title bar. When accessed, it looks like this.
When you select Browse All Versions, did you know that you could use the option key to change the "Restore" option into "Restore a Copy"?
Also, did you know that the document interaction menu also appears inside the version browser? Click to the right of each file name on the history stack and you'll find the option to "Delete this version". If you hold down the option key, that changes to "Delete Old Versions", allowing you to clean up the entire history at once.