Steps to reproduce:

1. Open attached project
2. Open scene "Scene"
3. In project tab click on "New Render Texture" and make sure that preview is enabled
4. Click on game view to make sure that it accepts keyboard keys
5. Press "2" and this will resize texture, call Canvas.ForceUpdateCanvases() and then Camera.Render()
6. Notice that render texture doesn't resize button
7. In scene view notice that canvas are resized

Additional steps:
8. Press "1" and notice that button isn't in the corner of render texture
9. In scene view notice that it should be in the corner

Reproduced with: 5.2.5f1, 5.3.6p6, 5.4.1p2, 5.5.0b5