Precursor, I had all resource inventory slots unlocked, and each slot was filled.
I had 1 stack of 20 copper, and 1 stack of 2. I needed to make room. I deleted the stack of 2, and it also removed 2 from my stack of 20 leaving me with 18.
This was replicated again several minutes later after I did the same thing with a stack of 20 pine and 2.
Side note: please make stack consolidation and item organization inside storage and inventory a thing. <3