Steps to reproduce:

1) Download attached project and open in Unity
2) Build and Run 'RotationTester' scene
Observe the cube and you should notice hiccups while rotation is applied

Expected result: Rotating cube should not have those hiccups(check attached video 'expected.mp4')
Actual result: Cube rotates with hiccups when Interpolate mode is set to interpolate (check attached video 'repro.mp4')

Reproduced with:
5.5.6f1, 5.6.5p2, 2017.2.0b7, 2017.2.0b11, 2017.3.0a7

Note that in some versions it's really hard to see those hiccups, but after some time they show up.

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Update:
This case was marked as a regression by mistake. After further investigation, small hiccups were seen in 5.5.x and 5.6.x too.