just as per thread's subject:
PCem 14 (but had the same problem with 13 and 12):
Windows 10 x64
When when I start a machine, any machine, through a batch file or link which makes use of the --fullscreen parameter, the aspect ratio (4:3 in my case) setting isn't honored.
Upon switching to windowed mode, the aspect ratio honors the settings.
Switching to full screen again, the correction is preserved.