The expectation of using Sketch > Rectangle fromCentre, is that it will remain centred on the original Creation Centre when changes are made to it’s dimensions.
This video clearly demonstrates that these expectations are not being met:
Of course I could be expecting too much?
This is the .shapr File:
RectangleCentreFail?.shapr (100 KB)
Hi Stan,
That is my expectation as well 
Currently rectangles are just 4 lines perpendicular to each other, once we will define them as a rectangle we will be able to do this.
Devs are already working on it, and next release (3.25) will most likely have this functionality.
Thanks Daniel, I have a workaround but it involves having a VERY steady hand, zoomed in close and trying to be precise to 0.01mm. It seems about 1 in 3 scores a direct hit. Looking at making a proper iPad/Wrist Support, there are plenty of options but seemingly very little that is rigid under all conditions.