While being recently at Gdańsk railway station, I was a bit bored and I took a leaflet from PKP (Polish State Railways). It contains the train schedule between Gdynia and Hel (there are more, for other routes as well) and it's obviously nothing special, except for a tiny detail on the back…
PKP Przewozy Regionalne leaflet
The last page contains an ad from Plus GSM mobile phone network and a fine print with an interesting bug:
There is a sentence: “50 godzin na rozmowy w tary?e Elastyczna 300…”, where the “taryfie” word has a question mark in the middle. Similar bugs happen from time to time with printing Polish diacritics, but in this case they happen to be fine.
The problem here is with ligatures. Some letter combinations are connected into one character (glyph) in traditional typography for aesthetic reasons. For instance, printing the two letters fi next to each other (like in “taryfie”) causes unpleasant blending of the dot above i with the tip of f. It's much better for a professional to design elegant ligatures in font and then use them with DTP software in print. In practice however, many fonts don't have ligatures at all. Besides, popular software like MS Office doesn't support them too.
The case above was apparently the result of copying the text between different applications or the font was changed – the original text contained the fi ligature and the destination system didn't have it. That's why it was replaced with the question mark.
In case you want to use ligatures in your documents, one of the DTP systems which support them is LaTeX.