Laser print damage to paper

I have just noticed in a correspondence file from 2000 that some of
the pages, most probably printed by a laser printer, now have very
distinct rust brown shadowing of the text on the back of the
page--you could read it quite clearly (with a mirror).  Given that
this file, and possibly many others with the same problem, are
designated for permanent retention under our Public Records Act,
this is potentially a serious problem. I'm unable at this stage to
identify the printer or the paper, but it only occurs on some
discrete items in the file.

Has anyone come across this before?  Any thoughts on what might
happen to these pages in the long term?

Robyn Waymouth
Archivist
Royal Women's Hospital
Locked Bag 300
Parkville 3052
Australia
+61 3 8345 3905


                                  ***
                  Conservation DistList Instance 27:8
                 Distributed: Thursday, August 8, 2013
                        Message Id: cdl-27-8-026
                                  ***