Homebrew PCBs

Hi all.

I mostly used Epson photopaper to make my quick-and-dirty
toner-transfer PCBs, but was tempted by a local electronics magazine
announcing an 'ideal' paper. Though the paper they sold was pretty
expensive, I'm quite sure the paper was just a good quality
illustration sheet. Anyway, I bought a couple of the 'originals',
and printed a board. Strangely there were some defects, so I used
another part of the sheet to re-print the board - same defects.
Worried, I re-printed on normal paper, and did _not_ have the defects.

The actual defects are difficult to describe. Here are a couple of
pics:

http://jcoppens.com/misc/laser1.jpg
http://jcoppens.com/misc/laser2.jpg

Left side is the magical paper, right is normal paper. As can be seen,
the left paper is better quality print (traces are 0.3mm), but some
strange 'explosions' occured. These seem to appear independent from
the place on the sheet, and _always_ on the better paper, never on the
normal one.

Any suggestions or ideas for identifying the cause?
John