That's not a knock against the app, but something you can actually fix - this would use the OSM backend, and adding your parent's address would take all of ten minutes if you care to do so.
On openstreetmap.org I found my address with no issues - I typed the address in the search box, and got a pointer on the map showing me where it is.
On OsmApp, the same exact query resulted in more than 19,000 results and the app proceeded to highlight them all on the map, which effectively means it's impossible to actually locate the address.
It's a nice proof of concept but there's a long ways to go.
There are no available map data that allow this except Openstreetmap.