Has this bug ever been fixed?
I just tried exporting my inventory after filtering for just standard cards, and all cards will show up in the export.
I have found a way to circumvent the bug which is filtering inventory by standard, then adding them to a new deck. Then export the deck and it will show only the cards that you just filtered on standard.
I do not know if this will still work with larger collections (I only just started inputting/testing on deckbox for my collection)