When importing BFZ lands, the count will only increment on the standard (non-full art) version of the card.
for example;

You have --
20x #262 (Full Art)
13x #262

You import --
20x #262 (Full Art)

In doing so, you will end up with --
33x #262
20x #262 (Full Art)

I believe the issue is tied to the identical card numbers ("Forest [full]" and "Forest" have the same card number, for example).

Can this issue be fixed?[/full]

I've mentioned the same issue some time ago:
https://deckbox.org/forum/viewtopic.php?id=29967

The older Sets Full art Lands where listed on deckbox with a different card number and on the cards as XXXa/XXX
while the newer sets have them with a tag for full art and when viewed in the inventory (or export) they are listed on a different line with same information. makes it confusing when someone has a large amount of cards and then needs to hunt through the cards to find the correct ones to adjust inventory.