Associativity error for Add() and Sub() operations

[DiffeRT]

AgeDurationTest.java:75

java.lang.AssertionError: 0.0.30 +(-) 0.0.1 -(+) 0.0.1 == 0.0.30
Expected :30 days
Actual :1 month 0 days

[DiffeRT]

a) On the one hand it is possible to have 1y 2m 30d
b) But on the other how to make transitions from 1m <-> 30d keeping in mind (a)