Hey andy, found an exploit where if you have 2 items and 1 is equipped but double tap to trade in the stack but then hit cancel instead of adding a new item to that spot, then you keep the equipped item but get credit for trading in both items.
Can confirm this
Have one item equipped
Have one other (or more) of that item
Tap on the equipped item on your tower
IT shows a stack of 2 or more
Doubletap and transmute the stack
Get credit for Every piece in the stack but the equipped item stays equipped