I'm using navit (latest trunk) on 64bit Linux (gentoo) with OSM maps - planet.bin as well as the europe-extract.
When I zoom out to "low" orders (starting around order 3-4), the maps become like the images you can find here:
http://tinloaf.de/~tinloaf/navit/
I didnt dig deep enough into the code yet to really know where this bug is located, but it seems like some items (i primarily tested this with highways) do get assigned different minimum orders at which they should be displayed, leading to items of the same type disappearing from the map at different zoom levels. A wild guess of mine is that this is an error of the osm2navit-part, because this (at least if i got the code that i read up to now right) seems to me to be the part where different itemtypes get there minimum orders assigned?
I'll tag it as "mapdrivers/OSM", since I don't get this error with the "Großer Reiseplaner"-maps...