To reproduce:
1) Open attached project and MyScene scene in 5.3
2) Search in Hierarchy for RightForeArmRoll
3) Check Rotation - it should be 0,0,0
4) Open the project in 5.4+
5) Check Rotation of the same object again

Expected: The value shouldn't change
Actual: It changes into 180,180,180

Not reproduced in 5.3.6f1, 5.3.7p4
Reproduced in 5.4.0f3, 5.5.2f1, 5.6.0b10

----------------

For the fix please follow the link below:

Transform.eulerAngles Returns A Different Value In Unity 5.4 Compared To 5.3

https://support.unity3d.com/hc/en-us/articles/115001622823--87600-Scripting-Transform-eulerAngles-returns-a-different-value-in-Unity-5-4-4p1-compare-to-5-3-5p8-if-transform-scale-is-negated