/trade - Item amounts shown in chat incorrect after trade

I made a trade with another player for 4 full stacks of TNT + 1 stack of 40, but after making the trade, it said in chat I received 5 stacks of 40 TNT, rather than 4 full stacks + 1 stack of 40. The items were ordered in the GUI such that the stack of 40 was first, followed by the stacks of 64. Not sure if this issue is Factions specific or also in RPG. See screenshot