When you have max Stash tabs and try to buy a new one, it should state that you have the max number or something to that effect, but instead it says that you don’t have enough gold for a new tab.
This is only on the hover over when you try to buy a new tab and have the pop-up window to Confirm or Cancel. It allows you to click the “+”, then gives you the pop-up with the amount of the new tab, when it should tell you have already have the max number and not give you the pop-up.