[mkgmap-dev] POI's disappear

I've noticed that showing POI's is somewhat out of my control. Example: I have campgrounds, using 0x4800, they will show up at the zoom level I expect, then I zoom in and some will disappear.  I zoom in more & they will come and go.   I suspect that Garmin is deciding that it isn't important and showing something else instead.   Is there any way to make this stick, or increase the priority?   It all works as expected on Qmapshack.   I'm using a Garmin Zumo XT & a DriveSmart. Thx Brad