How to reproduce:
1. Open the attached "1274892" project
2. Open the "SampleScene" Scene
3. Open the Timeline window (Window->Sequence->Timeline)
4. In the Hierarchy select the "Sphere" GameObject
5. In the Timeline double click on the recorded Clip
6. In the Animation window start recording
7. In the Animations Timeline move the Playhead to the 27th frame
8. Move the "Sphere" GameObejct in the Scene to record a keyframe

Expected result: The keyframe appears on the 27th frame
Actual result: The keyframe appears on the 26th frame

Reproducible with: 1.0.0, 1.5.0-preview.4 (2018.4.27f1, 2019.4.9f1, 2020.1.4f1, 2020.2.0b2)

Notes:
- The issue is reproducible only when animating a Timeline Clip. Does not reproduce when animating an Animation or Timeline track
- The issue will not reproduce if the Timeline Clip has a frame recorded on a 0th frame
- Recording in the Timeline on the 0th frame and then moving the Clip will not reproduce the issue
- Not having anything recorded on the 0th frame in the Timeline and then moving the Clip to the 0th frame position will produce the issue
- The issue is reproducible only when recording a keyframe at certain frames (for example trying to put a keyframe on the 20th frame will work as intended and the keyframe will be created at 20th frame but trying to create a keyframe at the 27th frame, the keyframe will be created at the 26th frame instead)