Includes memory card in 'internal memory' when backing up to memory card (Asus Transformer)

I have an Asus Transformer tablet where I’m trying to back up the internal memory to a Sandisk microSD. The application correctly deduces how much storage is used of the internal memory (the internal flash) and how much is used on the memory card. However, when I start a backup the application will then include the data on the memory card itself in the backup… and as I have tons of videos etc. on the card that’s not good (it’s a 64GB card I originally installed to save on space in the internal storage). It looks like although the application recognizes the memory card it is unable to realize that the /Removable directory on the root of the device is actually the mount point for the SD card. This of course makes it pretty much useless for backups… if I let it run it’ll presumably include its own backup in the next backup too! I have not found a way around this, e.g. some ‘leave directory/folder alone’ option. And of course it should really recognize a mount point by itself. I did search the FAQ but found nothing.