To reproduce:
1. Open attached Unity project "New Unity Project.zip"
2. Open "Scene" scene
3. In the hierarchy, locate Canvas --> Image
4. change either left, right, top or bottom value
5. Right click on the changed value and press "Revert Value to Prefab"

Expected result: the value turns back to the prefab's default value
Actual result: The reverted value changes to some random number and the opposite side's (right for left, bottom for top) value becomes the identical value, only negative (see user's attached video "2017-11-28 19-42-03.mp4")

Reproduced on: 5.5.4p2, 5.6.4p1, 2017.1.2p3, 2017.2.0p3, 2017.3.0b11, 2018.1.0a6

Verified fixed on 2017.4.5f1