Please follow the steps bellow to recreate the bug:
- select any card, and to change its Style properties click on the box icon
- press ctrl+Z or cmd+Z to undo the transformation
If you check the cards ‘created value’ under your profile pictures you can verify that you are in fact one card less. If you have a clean account and have no cards, and you follow those steps on the introduction space, you can get a negative value giving a free user additional cards.