Steps to reproduce:
1. Start a new project
2. Select Main Camera game object
3. Drag and drop the Field of View Slider to any other value distancing from the first one (or any other slider)
4. Undo the slider change
5. Notice that instead of going back to the previous value, it will go back to a previous value by small increments in the way you moved the slider

Expected result: editor UI slider should not record slider drag steps when undoing changed value
Actual result: slider undoes last Editor GUI Update instead of the value before starting to move the slider

Reproduced in: 2018.1.0a7, 2017.3.0b11, 2017.2.0p3, 2017.1.2p3
Not reproduced in: 2017.1.2p2, 5.6.4p3
Regression since: 2017.1.2p3