I installed primo last week, and it seems to be ok except when going thru tunnels. I am not too sure if it has to do with the signal itself, or just that the map actually shows it as a tunnel. I went under a large bridge and it was no problem I thinnk it has more to do with the "tunnel" as is shuts off immidiately as the arrow icon hits the tunnel on the navi.
I've never noticed my primo turn off before while driving but have notice it restart itself, Some tripe it doesnt happen atall and other a couple of times as when I look at the screen its on the main menu.
I havnt thought about it being when i go through tunnels tho, So will pay attention next time.