Glaze defect after decal application, why?

[also posted to Clayart]

Hey everybody ... no it's not Dr.Nick, but hey anyway.

I've got some defects on some glazed ware after decal application and
was wondering if anyone can help diagnose what I've done?

I used ^04 (cone-0-4) bisqued plates which were glazed with a Gare 1700D
clear glaze. The ware was fine, as expected after this.

Next I applied some digitally made decals (no idea about the
constituents of these, but have used them in the past on some mugs
without problems) to 850 degC (3h30m to 600 degC and then full speed to
850 degC in a large top-loading electric kiln). Two decals on the top
face of the plate, one on the rear, centrally placed, with my logo.

The decals have worked fine, reasonable colours, a couple of defects on
one piece (but they seem to be due to pinholes in the underlying ware).
However, there are some unexplained "tracks" on the reverse of both
plates. The tracks go across the central portion and seem to be
interrupted by the foot; one of the plates has a single track on the
bottom at the rim, but this doesn't line up with the tracks inside the
foot. Some pictures are available at
http://barefoot-ceramics.com/defects/ ; sorry there not great, I had to
use the light reflection to highlight the defect. In the second image
(2354) the lump at the bottom right is a stilt mark. For anyone that
can't make them out ... the tracks look like the effect you get with
water on a cobweb except that they are discontinuities in the glaze surface.

What I'd like to know is if anyone knows what caused these tracks and
then what to do to prevent them.

My suspicion is that it's some release of gases from the decal ... but I
haven't a clue and can't really afford to waste more decals and plates
trying things; especially if you know the answer!

Thanks muchly,

pbhj