TFT Bug/design flaw

When your board is overflowing (IE your inventory was full, and you grabbed a unit from carousel) if you combine or sell a unit in your inventory (making a spot available), it just randomly pulls a unit from board.

Expected behavior would be to pull the most recently added unit (the one from carousel), nope it just randomly pulls one which has caused me to lose a game several times because I was busy rolling and didn't notice until round started.