In 18w31a, the %= operation was changed to use Java's Math.floorMod instead of %. However, the /= operation still uses Java's / instead of Math.floorDiv, which is inconsistent.

To reproduce:

Create a new world:

Run the following commands:

/scoreboard objectives add test dummy
/scoreboard objectives setdisplay sidebar test
/scoreboard players set n test 3
/scoreboard players set a test -5
/scoreboard players set q test -5
/scoreboard players set r test -5
/scoreboard players operation q test /= n test
/scoreboard players operation r test %= n test

With a consistent division algorithm, a = n*q + r, but this is not the case here.