[mkgmap-dev] possible bug? mkgmap freezes with lines only routing style

i'm trying to create a lines-only routable map. from a certain amount of lines in the style mkgmap starts turning out 2 empty img files (empty means 0 bytes, not empty maps), then memory usage freezes pretty much, cpu usage oscillates wildly and nothing more happens. this problem is tied to --route, leaving the option out turns things back to normal. a certain amount of poi's in the style solve the problem too - with some lines for cities in the points file everything works as expected. it almost feels as if mkgmap "needs something to do" between all the roads. any ideas?