[mkgmap-dev] Garmin "Feature" or bug?

I have a suspicion this is a Garmin "Feature" rather than a bug but thought it best to check. I have an Edge 605 which I'm using with routable maps created with mkgmap r806. If I go to the menu option to Find | Places then my 605 lists all places within a radius including those on the gmapsupp.img. There is also an option to enter a name manually but if I try this it only gives me place names from the gmapbmap.img. If I remove the gmapbmap.img and try again then the 605 crashes which is why I suspect it's a feature Can anyone shed any light on this Thanks Paul