Sudden washed out picture in Book

Some pictures that looked OK for a long time (say weeks) suddenly turned washed out in the Book (album) I created.

I have a Project for which I created a Book in Aperture weeks ago, and I have already ordered 2 books without any issue.

About 2 weeks ago I had some of the pictures in the same Book suddenly appearing washed out. These are always panoramic pictures created with Canon PhotoStitch and PanoEdit, but not all of my panoramic pictures had this problem.

When I open these picture in Project, they appear OK for 1 or 2 seconds, then appear washed out as well.

The only way I found to recover is to reimport the original picture into the project, apply adjustment again, and copy it to the book.

This issue seems to appear randomly in time but always with panoramic pictures and I have no clue what triggers this white cast overlay.

Does anyone have a clue about what triggers this issue, and how to solve this?

Thanks!

Philippe