Steps to reproduce:

1. Open attached project
2. Open scene "OnRectTransformDimensionsChange Callback Repro"
3. In hierarchy, fully expand "Canvas" GO, select "Image (1)" and focus it (by double clicking)
4. In scene view, click and drag image outside of its parent and notice that sometimes OnRectTransformChange is called

Additional steps:
5. In scene view, click and drag "Image (1)" pivot point
6. In inspector, notice that dimensions of the RectTransform are changed by a small number and as a result OnRectTransformChange callback is being called

Reproduced with: 5.2.4f1, 5.3.4p3, 5.4.0b15