Mapsource is discontinued unfortunately: Garmin doesnt support it anymore.
I made a search in Belo Horizonte and it crashed, probably MS is not good to handle successfully City Navigator maps anymore. I guess it works fine in Basecamp and may be Mapinstall could send img correctly to devices.
I'd try it.
It happened with CNE recently with Italy map, we made some tests too and in Basecamp it worked fine.

Edit: tested in Basecamp, zoom is buggy, Some tiles dont show and appear gray zooming.
Something weird in it, IMHO is buggy.

Edit2: new version posted on 19-1.2013 works fine