I feel like the second issue ack mentioned (duplicating cards, if I understood correctly) is still a thing. Here's a log of actions I took with an empty Deckbox inventory.
1. Hit "Add cards" button
2. Type Vaporkin, hit enter. 1 Theros Vaporkin is in my inventory (as expected).
3. Hit "Add New Row" button
4. Change the added Vaporkin row to Conspiracy, increase number to 3. Hit Save. 1 Theros and 3 Conspiracy Vaporkins in my inventory. (As Expected)
5. Hit "Add New Row" button
6. Increase number of Theros Vaporkins in the newly added row to 3. Hit Save. Now there are two rows of 3 Conspiracy Vaporkins each in my inventory (for a total of six, although only 3 were added in step 4), along with 4 Theros (as expected).
Inventory now lists 10 cards, 3 distinct. (Expected 7 cards, 2 distinct)