Exporting to pdf gives problem with a font

In order to let my flyer to be printed i need to export it to PDF. But i have a slight problem: a small part of the text is getting a white line around it.

Here is the pdf: <http://diod.dommel.be/postxmos/pxmos_5_A6_highres.pdf>

As you can see, the first P and the last S of the vertically inverted "POST XMOS" got some white around it, while it shouldnt have that.
Ive got no idea why its doing this, cause i have used the same font before and it exported just fine to PDF(the vertically inverted text too).

EDIT: I'm using Photoshop CS3 btw

You're seeing stitching as a result of flattening the PDF. If you turn off smooth line art in Acrobat/Reader preferences it will go away on screen.

It shouldn't print but I would resave the PDF using the prebuilt press setting which uses Acrobat 5 compatibility thereby retaining the transparency in the PDF.

Bob

Turning off smooth line art works, thanks :)

I dont think i'm "allowed" to save it with the prebuilt press settings, cause on the printer's site was a "flyer.joboptions" file which i had to import into photoshop and it said to save it using those options.