System hangs after closing a DOS program launched from Windows 3.0 w/ PC-DOS 4

[barotto]

When a DOS program launched from Windows 3.0 (386) gets closed, the system hangs with a black screen and a blinking cursor instead of returning to Windows.

[barotto]

If Windows runs in PC-DOS 4, after calling INT 21/4C (terminate program), the CPU gets stuck in an infinite loop waiting for something that never happens.
If Windows runs in MS-DOS 6, INT 21/4C terminates normally and the system returns to program manager.
If Windows is started from the 4-quad romshell the issue does not happen.
This needs to be tested on real hardware.

[LuiZapper]

On real hardware for instance on model 2121 (386SX-16 CPU - 6MB RAM) using IBM DOS 4.00 (PT-BR) and Windows 3.0 (PT-BR) this issue doesn't happen, although some command line executions can cause "execution errors" like when executing "MEM" command. In any case, returnning to program manager was successful.

[barotto]

Thanks for reporting!
I actually expected IBM DOS 4 + Win 3 to work correctly as it was a standard setup on the PS/1.
This is a strange issue and I'm not really sure how to debug it, though I suspect it might have something to do with the PIC.