OK, this is a very odd but simple to reproduce bug that happens when
anchoring controls inside a panel or any inherited class from
ScrollableControl.
Symptoms
The designer will adjust the width of a control to a different width than
set when it's placed on a scrollable control where the vertical scrollbar is
visible from within the designer and it's anchored on the right.
How to reproduce
1 - Place a panel on a form.
2 - Set the panel's AutoScroll property to 'true'
3 - Put 2 buttons inside the panel
4 - Move button 1 to overlap the bottom of the control to force the vertical
scrollbar to appear.
5 - Anchor button 2 to the right of the panel
6 - Save and close the form.
7 - Open the form in the designer and notice the width of the anchored
button has been adjusted.
8 - Adjust the size of the FORM not the panel. Repeat step 6 + 7 noticing
that the buttons width reduces furthur for each close and open of the form
when changes are made and saved.