Basic Map shows above OSM Map

BaseCamp can currently only display one map at a time, so I am not sure what is going here.

Are you sure it's BaseCamp's global map you are seeing along with the OSM map, and not the OSM maps's base map?

BaseCamp will not start if you have no maps installed, so I wouldn't recommend removing BaseCamp's global map.

This is probably a better question to ask on the OSM forum. http://forum.openstreetmap.org/index.php

FWIW I had a similar problem with BaseCamp using transparent or semitransparent maps I made with cgpsmapper. It was my map's background I was seeing. Try hitting cntrl-G. That should clear the video for the top level map. cntrl-G again should re-draw it. Also, see if the same problem occurs in MapSource. In my case, it didn't.

Just checked to see if the problem still occurred. Can't see it now, so I guess it's specific to an earlier BaseCamp version. Are you using the latest BaseCamp?

Thanks to both of you for your answers.
Obviously Falagar is right: As a beginner in basecamp as well as in OSM I did not know, that the OSM Maps have own base maps: But the following tests show this: I have 2 different OSM Maps from different sources loaded on an USB Stick and show them in Basecamp..Then, in each of this Maps, I pressed Ctrl G, which means Base Map only ( In German: Nur Basiskarte). I combined this maps together with its basemaps and attach them here.
A1 shows the area reasonable, only a black line is not correct. A2 is unreasonable, a part of the village is under water, obviously the coast line has been copied from the coastline in the base map and the Autoroute also is at a place where there is in reality no autoroute.
I have basecamp 3.2.2 in German, Map source I dont have.
To look to a OSM Forum is a good tip, but I have until now no knowledge of this forum and they certainly want to know, where this two maps are from. So this may need some time more.

Sorry, A1 Upload failed. I hope it gets through now.

This is not a BaseCamp problem. You should take this up with your map providers.

This is not a BaseCamp problem. You should take this up with your map providers.

You gave me the link to the OSM Forum already, I followed this advice and found out, that it is there a known issue. So, in principle you are right. But not completely: It is a fact, that the maps which have in basecamp this overlay problem, are displayed in the handheld oregon 450 itself without this problem. So Garmin has an algorithm who avoids this problem. But I understand, that they don't put very much effort to solve problems with the maps of their competitors.

You gave me the link to the OSM Forum already, I followed this advice and found out, that it is there a known issue. So, in principle you are right. But not completely: It is a fact, that the maps which have in basecamp this overlay problem, are displayed in the handheld oregon 450 itself without this problem. So Garmin has an algorithm who avoids this problem. But I understand, that they don't put very much effort to solve problems with the maps of their competitors.

Either that, or your map providers should try to more effectively comply with Garmin's standard. From the looks of the images you attached, the maps had problems with background polygons and coastline flooding. Both of those are known issues with some versions of OSM compilers, but those issues need to be addressed by the map makers, not the software used to display the map.

If you have a PC and BaseCamp up and running you should be able to download a MapSource upgrade and have it install correctly. You could then see if the problem occurs in both viewers or if it's specific to BaseCamp.