Reproduction steps: (see video)
1. Open the attached project
2. Open the available scene
3. Attempt to resize the button in the canvas

Result: Button Rect Transform is centered while the button is not

Note: Making any other change in the editor, sets the button to it's proper place

Reproduced with: 5.5.0a1, 5.4.0b21, 5.3.5p3, 5.2.3p3
Not reproducible: 5.1.3p3

Tested on: Windows 10

Regression since: 5.2