The addCard command, called from a TaskBoard in the PreviewPane, is also executing for the parent TaskBoard. That results in a JS error.
A JS error is thrown and a card is not created.
No JS errors should be thrown and the card should be created.
When a card in the TaskBoard is moved if the server returns an error the move could not be prevented. Thus, the card is rendered in the new position.
Although the server returns an error the card is moved to the new column.
Moving the card should be prevented when there is an error.