When you use the Snap feature in Windows to resize the editor window (for example by dragging the resize cursor at the top of the title bar up to the top of the screen), Sublime doesn’t remember the ‘snapped’ position, but instead the last manually resized position.
If you manually resize the editor window by a pixel or two after the snap, everything works as expected. I’m assuming Sublime is subscribing to certain window events which get fired when manually resizing, but don’t get fired by a Snap resize.
An exception to this is maximising: if you drag the title bar itself (where you are seeing the ‘move window’ cursor rather than the ‘resize’ cursor), the editor does open in the maximised position on next run.
This is obviously a fairly minor issue, but would be nice to have fixed when Sublime reaches the polishing stage!