With Type 3 fonts the function pdf_mark_text_glyphs marks entire text with all fonts assigned to it due to glyph variations. It must mark exact text portions corresponding to each font. Diagnosed with the test file of the bug 688967. This problem doesn't look highly important, but we'd like to fix it someday.
Passing to Ken since he handles pdfwrite from now.
Bug still reproducible in Ghostscript 9.03
I have absolutely no idea what this bug is saying, it makes no sense to me at all. The observed behaviour of the routine pdf_mark_text_glyphs doesn't do what comment #0 seems to say. I'm closing as 'wontfix', if whatever it is ever becomes important, we'll fix it then.