There might be a workaround for this, and--like the feature itself--the workaround is also dependent on Google Maps.

The GPX Driving Directions Web Service (which Maemo Mapper uses for routes) uses maps.google.com by default, but you can also change the "top-level domain" so that, for example, you can use maps.google.de if you want. If you can enter your small streets in maps.google.de and get directions fine, then here's the workardound to your problem:

At the top of the "Download Route" dialog box is a text field for a URL. If you add "&tld=de" to that URL, then Maemo Mapper will instruct the web service to use maps.google.de instead of maps.google.com. The result will be the same as if you tried to use the directions feature of maps.google.de. A side effect (for better or for worse) is that, since maps.google.de uses German as the language, all direction information will be in German.

That's also the workaround to get directions in your own language, by the way.

(Yeah, I know, I'm a bad person, I should document this somewhere. Well, this will have to do for now. )