[GAMEPLAY] Losing the first item when you finish your next item

When you go back to shop and finish your second/next item, it would automatically sell your first item. You still can undo it if you realize it before too late, like get out of the range of the shop. use your item/ability, etc.

 1. Buy first item
 2. Farm and/or kills to get enough gold for second item (finishing parts) 
 3. The first item automatically sold without any interaction from the player

It happened to be 3 times already. In the first one, I didn't know it happened and that bug had cost me a win game during a tournament that my team entered. Now that I'm aware of, I'll just undo it in shop and everything will go back to normal and then I can buy it again. It doesn't happen always but I'm always double check my items before leaving the shop. Last time happened November 5th, 2016, patch 6.21.

P/s: Please excuse my English knowledge.