I'm not sure if it qualifies as mixing logical levels but I once tracked down a printer bug where the PDF failed to print.
The culprit was an embedded TrueType font that had what (I think) was a strange but valid glyph name with a double forward slash instead of the typical single (IIRC whatever generated the PDF just named the glyphs after characters so /a, /b and then naturally // for slash). Either way it worked fine in most viewers and printers.
The larger scale production printer on the other hand, like many, converted to postscript in the processor as one of its steps. A // is for an immediately evaluated name in postscript so when it came through unchanged, parsing this crashed the printer.
So we have a font, in a PDF, which got turned into Postscript, by software, on a certain machine which presumably advertised printing PDF but does it by converting to PS behind the scenes.
A lot of layers there and different people working on their own piece of the puzzle should have been 'encapsulated' from the others but it leaked.
The culprit was an embedded TrueType font that had what (I think) was a strange but valid glyph name with a double forward slash instead of the typical single (IIRC whatever generated the PDF just named the glyphs after characters so /a, /b and then naturally // for slash). Either way it worked fine in most viewers and printers.
The larger scale production printer on the other hand, like many, converted to postscript in the processor as one of its steps. A // is for an immediately evaluated name in postscript so when it came through unchanged, parsing this crashed the printer.
So we have a font, in a PDF, which got turned into Postscript, by software, on a certain machine which presumably advertised printing PDF but does it by converting to PS behind the scenes.
A lot of layers there and different people working on their own piece of the puzzle should have been 'encapsulated' from the others but it leaked.