Mac OS X Desktop Wallpaper broke after switching from iPhoto to Aperture — Fixed!

Summary: If you've deleted your iPhoto library (e.g. after switching to Aperture) and your desktop wallpaper preferences have stopped working properly thereafter, recreate the iPhoto library (with the same name as before) and it should fix the problem.

I recently tried out Aperture (previously using iPhoto) on my MacBook Pro after purchasing a Canon 450D (in-depth review), and, after deciding I liked Aperture more than iPhoto, I migrated all my photos from iPhoto into Aperture and deleted my iPhoto library completely.

The result of this (apart from the obvious intended one of my photos being in the Aperture library) was that my Mac OS X desktop wallpapers stopped working properly. Going into the System Preferences app, and into the Desktop & Screen Saver pane, I discovered the following:

• My custom folders were no longer listed in the selection slider on the left – all that remained were the default Apple folders (Apple Images, Nature, Plants, Black & White, Abstract, Solid Colors [sic], Pictures Folder) and my Aperture Projects... twice.
• Attempting to open either of the Aperture Projects folders caused the second one of them to open (I could click on either, but it would always open the lower one in the list) – selecting any of the projects/albums worked fine (almost... see below)
• I could no longer add/remove folders (the +/- buttons at the bottom didn't work).

This bugged me since I had previously been using a few folders that I manually added pictures to for wallpapers... so at first I was mildly annoyed and after logging out / rebooting didn't fix it I set up a Wallpaper smart album in Aperture to much the same effect as my custom folder. Fine. Almost...

Every time I went back into the Desktop & Screen Saver preferences, my wallpaper selection would revert (for all active monitors) to the Apple Images selection. I think this also happened on reboot (can't quite remember) and when I plugged in my second monitor (which I only use at work... and thus happens about once a day).

Completely separately and coincidentally I was helping my girlfriend use iPhoto on her laptop (over IM), and wanted to open up my version of iPhoto so I could remember where a menu option was; this required me to create a new iPhoto library. Inadvertently I'd just fixed the problem. I noticed the next day and went into the System Preferences to discover now that the iPhoto Albums had been reinstated in the list, the custom Folders list was also back (along with the ability to add/remove them and the settings surviving reboots and unplugs).

It may be important that I used the same name for the iPhoto library as the previous one (i.e. just the default), so if you've got the same problem it may be important to pick the same name.

I'd be interested to know if there's a "correct" way to delete the iPhoto library that doesn't break the desktop wallpaper settings when switching to Aperture, but for now I guess I'll leave the empty library in place.