I have also seen this behavior in the Windows 10 style. Not sure why it happens, but it's a minor issue for me.
When the All Apps menu is opened, it is left justified of the Start button, and the first time opening the Start menu following the use of the All Apps menu, the Start menu is right justified of the Start button. The second time it is opened, it is centered again. The Windows 10 style appears to be the only style with this behavior.
Perhaps there is an easy fix for this.
Basj, please report this to the Dev's.