Why is "round down" returning fractional values when used on Get Items In Stack?

When I use "round down (Get number of items in stack)" on a stack of 1, I get 1.01. When I use it on a stack of 64, I get 64.064. That's not even mathematically consistent. What am I doing wrong? An earlier version of this code was working, it only broke once I tried to make an exception to allow empty slots to be filled. I rewrote it all to focus on just that case and now it deletes items without placing any. I think this is because of the fractional value, so I implemented a round down... but it seemingly does nothing.