Router can make path through military areas, where entry is prohibited. For example, route from "Sedlec u Radonic" to "Carlsbad" (both Czech Republic) will lead through "Vojenský újezd Hradiště", but police will approach you very quickly and tell you that you need to go round :)
Otherwise, thank you very much for this great service!
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Oops! That looks like an error in the OpenStreetMap map data: I've raised the issue on OSM and hopefully someone local can fix it.