This is a pre-release version of Microsoft Windows 3.1 that was shipped to testers in approximately July 1991.
Microsoft Flight Simulator issues
In a series of e-mails between programmers at Microsoft from July 3rd, 1991, it is shown that while testing Microsoft Flight Simulator 4.0 in Windows 3.1, although it runs within an MS-DOS session, not only is it slow, but also experiences severe problems with color mapping (citing also the fact that the same user submitted a bug report for this problem).
It was also mentioned that there was yet another bug (one that was harder to reproduce) that resulted in major screen draw problems.
The same user also found that it scrolling is much smoother when run in an OS/2 DOS window than under Microsoft Windows 3.1.
