Some photos not showing up in media selector

A little puzzle.......

I recently purchased an iPad with photo display in mind. The easiest way to get pictures from my iMac to the iPad is through iTunes. Works fine. I use a couple of smart albums to select only the highest ranked photos, and those albums I select in iTunes to sync.

But then I found out some photos are missing. Looking at the numbers in the iTunes album browser this became obvious. For instance, a smart gallery containg 45 items would show up in iTunes with only 27 items. This problem is not limited to iTunes, as the media selector in Pages shows the same number.

I first repaired the database and the permissions, to no avail. I then found out that changing the edited pictures in Aperture seemed to help. Now all my favorite pictures are .tiffs produced by NIK's plugins. Some of those I worked on a little in Aperture, f.i. cropping or altering the white balance somewhat. Those images are the ones missing in iTunes. I was able to add a missing picture to 'iTunes' by removing the adjustments (which off course I do not want to do).

Unfortunately, this rule has an exception (like any rule in life, expect in computing) with a smart gallery full of cropped NIK files. So I am still a little lost as to exactly where the problem lies. Anyone have similar experiences?