I was recently given three identical Transcend brand 8GB SDHC cards. When I initially inserted these cards (one at a time, as I have only one SD slot on my PC) and mounted them, there was some confusion probably due to the fact that they really were identical - right down to the UUID and lack of volume label.
I reformatted all of them with mkdosfs, giving each a volume label and verifying that they then also had unique UUIDs.
Now if I insert one card and start mnttool I can hover over the button for the card and it displays the volume label. However, if I remove the card and insert one of the others then click the refresh button, wait a few seconds and again hover over the button for the card it will still display the volume label from the first card, not the current one. If I close and restart mnttool, it displays the correct volume label.