I use DroidWall to prevent apps going to the internet when I'm on GPRS.
I added both offical Maps and Locus Pro to the white list, so that both of them can use the internet. Maps work OK, search, address loading etc works good.
If I disable the firewall, Locus works OK on GPRS. But with firewall enabled in Locus both search address loading don't work for me when on GPRS. But the "Compute route" works OK even with firewall enabled! So some parts of the Locus can access internet through the firewall and others can't :)
hmm interesting :) I use for address one more method against other internet connection. Firstly I check if system have access to internet by some system method. Is so, then i connect. This is faster when no connection is available. And looks that this can cause some troubles ...
I enabled only Maps and LocusPro, so may be the system method returns false for you because System process is not in the white list