Windows [1.6.9] Splitting stacks in half sometimes leads to loss of items

[GoudaQuiche]

I have a stack of 37 blueberries, I shift right click the stack, I get 19+17 = 36; I shift right click the 19 stack from my inventory, I get 27+8=35. I lost 2 blueberries. If I keep right shift clicking odd values, I will lose more and more ?

I do not know how half 37 never gives 18 but 19 and 17; I do not understand how 19 halfed ends up giving a 8.

 

[GoudaQuiche]

Here is a save file. Open the light green chest to reproduce.