Finally got a chance to do the update and rebuild. Works like a charm.
Thanks so much (once again)!
I've now identified the cause of this and fixed it. Please open jAlbum and select Tools->External->Tools->"jAlbum core update" to apply the fix. Restart jAlbum when prompted. The splash screen should say 25.1.2. You need to issue a "Force rebuild" to have jAlbum reprocess all images.
(The cause of the problem was that the Auto correct filter wasn't being cloned deeply when applied to multiple threads - it shared common data structures that polluted each other. I now implemented a proper deep clone.)