Deeply weird font kerning issue

[Steve Rickaby]

FrameMaker 7 for Mac, Illustrator CS2, OS X 10.4.11.

I appreciate that this is not specifically a FrameMaker issue, although FrameMaker is involved. It relates to a truly strange last-minute 'gotcha' on a production run for a book.

The book contained diagrams that were created in Illustrator, saved as EPS files, imported into FrameMaker and a .ps and press-quality PDF created from that via Distiller. The diagrams used Frutiger Roman and Monospace 821 for text.

On checking the pre-press proofs, the production editor spotted some text 'corruption', in that some legends in one diagram in a test print from the final PDF had very uneven kerning, even to the point of overlaying characters. The 'corrupted' legends were words bracketed on either side by guillemets, the double diagonal brackets that I believe the French use as quote marks (they mean something special in UML notation, which was why they were in the diagram).

I went back to the original diagrams, which looked fine. Ok, I thought, invisible 'corruption': I can fix this by replacing the problem text string. So I did, then reimported, re-cut the PDF and test printed it. And the 'corruption' had moved to the next instance below of a word enclosed by guillements. 

Right, I thought, I'll replace that and all will be well. You can probably guess what happened next... the 'corruption' moved again.

There were four strings set in Frutiger and enclosed in guillemets in the diagram. When I got to the last one and replaced that, I though all would be well, but what actually happened was that the 'corruption' moved back to the first text instance.

At this point I started to feel a little like Mickey Mouse in the 'Sorcerer's Apprentice' sequence in Disney's 'Fantasia'.

To cut a long story short, I figured that the problem, whatever it was, was related in some to the number of guillemet pairs in the diagram. My fix was therefore to make one of the rectangular objects in the diagram solid white fill, duplicate the last guillemet-braced legend on the screen, and *hide it* behind the solid white block.

It worked. But why?

-- 
Steve