Aperture 3.5 does not open all files in external editor (PS CS6)

When I select several photos in Aperture (which are parts of a panorama serie for example) and click choose to open them in the external editor (here Adobe Photoshop CS6), only a random subset are opened.

Aperture warns me if I want the (for example) 14 pictures to be exported for edition, I confirm, but I end up with only (for example) 9 photos in Photoshop. The missing ones can be any photos (not necessarily the first or latest).

Note that 9 is not an upper limit, I once opened 23 photos and only had 21 in Photoshop opened.

If I again select those same photos and choose to export them (either as PSD using the same format as with the Editor command, or asking for the original that was created for the external editor) to a folder. Then when I open all the photos at once form the finder (or Bridge) to Photoshop, I have all the photos in Photoshop. So Photoshop has no problem opening the files.

Do you have the problem too? How do you solve it?

For the time being I manually export the files, open them from the Finder, stitch them in PS and reimport the result in Aperture.

A bit tedious... If there is no work around, I will try to fiddle with some automation...

Final note:

PS CS6, Aperture and OS X are all at there latest respective versions (i-e respectively: 13.0.6, 3.5.1 and 10.9.2)