That does not sound like a bug to me. Rather it is Garmin trying to limit people who want to perhaps use multiple downloads to share software with others who have not paid for it. BTW, I am NOT suggesting that the OP falls into this category.
But, the maps you buy (e.g. Lifetime Maps) are tied to the GPS device, and Garmin allow you to download the maps to a computer (now limited to one computer) so that you can use Basecamp software. If the OP wants to use Basecamp on multiple other computers, then all he has to do is connect one of his GPS devices (for which he has paid for map updates on)to the computer and Basecamp can access and use the maps that are held on the GPS device.
I do not see that as unreasonable. Just Garmin protecting its intelectual property. Indeed, it may not be Garmin forcing the issue, but Navteq as I believe the mapping is Navteq not Garmin