Not sure if this a bug or just me being misinformed about how the backpacks work in the soldier-inventory screen.
Whenever I drag an item in the inventory of a soldier, the full TU-cost is always deducted, even if I put the item back into the exact same slot/position in the inventory, basically deducting it at the start of the drag.
The TU cost of moving things should be displayed before you move something, or at least less than putting things in or grabbing things from the floor, the spent-TU counter in that screen is not very informative because it only shows the deducation that has already happened, which in my case ment nothing was moved around as I put the grenade right back where it was after noticing it costs me 10 TU to even touch it.
At least I had to learn the hard way that sorting a backpack for OCD reasons would cost me a whole turn for that soldier, so there is that.
BTW awesome game, I love it so far! Keep up the great work