The iGO Nextgen Pongo skin has a map switcher.
I use NNG and HERE maps, but mostly NNG maps.
When I block a street from the planning, it saves it. But when I switch to HERE and then back to NNG, the street I previously blocked is no longer there. So after changing maps, it deletes it and doesn't remember that I blocked a road/street.
In principle, it stores this in the save//// ROADBLOCKS file.