Photoshop Elements 4 for Mac, iPhoto, and iMac OS X 10.5.1

Photoshop Elements 2 won't run under Mac OS X 10.5.1 "Leopard" so I bought
Elements 4.

I have only seen this with B&W photos, but that may be because I haven't been
working with anything but B&W.

After Photoshopping and saving a picture, sometimes the picture will appear
in iPhoto darker and with higher contrast than it did in Photoshop.
Sometimes it's all black. EXCEPT: When the picture in iPhoto is expanded to
max, it suddenly changes to a strange format: it looks superficially like a
B&W negative, though it isn't a negative, just high contrast and low dynamic
range.

Once this has happened to a photo, there's no way to recover in iPhoto except
to revert to original and start editing from the beginning.

A workaround is to save the photo from Photoshop in TIFF format to a folder
external to iPhoto and then import to iPhoto. (Saving as a JPEG and
importing to iPhoto produces the same distortion as saving directly to
iPhoto.) What's wrong with this workaround is that the TIFF has to replace
the original scan in iPhoto, in addition to being a pain.

Can anyone suggest what might be going on here?

--
John Varela
Trade NEW lamps for OLD for email.