/= assignment operator breaks type system

while this works:
groovy> long d = 100L
groovy> d = d / 33L
groovy> d.class

Result: class java.lang.Long

the following breaks the type system and produces a Long that is a BigDecimal!

groovy> long d = 100L
groovy> d /= 33L
groovy> d.class

Result: class java.math.BigDecimal