After writing my previous post I did some research to confirm what I was talking about. This is what I found.

"Place photographs in plastic sleeves void of PVC, which can be purchased at photo supply stores." and "Use plastic sandwich bags for a good, inexpensive alternative to plastic sleeves." - http://antiques.about.com/hobbies/antiques/c/ht/00/07/How_Properly_Store_Old0962933988.htm

Also,

"2. PVC Pocket Pages
Not all plastic album pages are harmful, but one type, made of PVC, or polyvinyl chloride, has shown a strong tendency to damage photographs. You can generally identify PVC by its smell. Most people say it reminds them of a beach ball or new shower curtain. After several years, the PVC starts to release some of the chemicals used in its composition. These oily or sticky substances can stain photographs and frequently causes them to stick inside the pocket, making them impossible to remove." - http://www.kodak.com/US/en/corp/membersGallery/archiving/pagesToAvoid.shtml

I may have been wrong when I attributed the problem to acid. That, I guess involves storing in paper envelopes or wood boxes etc. None the less, there may be something to consider here.

Would be interesting to find out if anyone knows whether this applies to chips and the pages some of us store them in. Are pages and AirTites archivically(sp?) safe?