Steps to reproduce:
1. Open attach file.
2. Open Scenes -> Test scene
3. Open animation window pick any frame except frame 0 and rotate "TestCube" with record button active
4. Inspect frame 0 notice that Ratiotion.z isn't set to 0 instead is set to around -1.5
5. Delete all keyframes and select "TestCube" child "Empty" record new animation the same way as first
6. Inspect keyframes at frame 0 notice that rotation.z is set to -80
7. Delete all keyframes and select "Empty" child "ChildCube" and record new animation the same way as first
8. Notice that at frame 0 all rotation value are set correctly at 0.

Workaround
Before starting recording, add objects rotation using Add property in animation window.

Reproduced with:
5.5.0b9
5.4.2f1
5.4.0f3
5.3.4f1
5.2.4f1