Steps to reproduce:
1) Open the attached project in Unity (rotation_bug.zip).
2) Open scene 'test'unity'.
3) Select the cube in the scene.
4) Try rotating it around the Y and Z axes in the Inspector.
- Everything should work as expected.
5) Now set the rotation around X axis to 90.
6) Rotate the cube around Z axis in the inspector.
- Notice how the cube rotates around its local Z axis, unlike when rotating around X and Y axes, the object rotates around global axes.

Expected result: object rotates around global axis.
Actual result: object rotates around its local axis.

Note: this issue is only visible, when either rotation around X or Y axis is not equal to 0.
Note#2: this occurs with game objects of any type.