I'm not sure if this is related, but I get those same green dot patterns with Tandy GW-Basic in screen 3 or screen 5 (160x200x16 and 320x200x16 modes). Using the exact same basic.exe on a real Tandy (or with PCjr cartridge basic) does not result in the patterns. I'm using the official 0.74 version for this.

The test program is

10 CLEAR,,,32767
20 SCREEN 5
(or screen 3)

In both cases the dots result and commands are no longer executed after the program is finished. It is possible to clear the screen again after setting the mode and the program will continue to run fine until it's done, but once done enter commands does nothing further.

That problem no longer occurs in the Tandy mode in the SVN as patched in this thread.

It still doesn't accept commands after switching though (machine=tandy)

Tandy GW-BASIC appears to be unresponsive to commands when it's in mode 8 and mode 9, because there's no problem if a program uses those modes but ends in some other mode. Adding support for M_TANDY16 in GetPixel() might fix the problem, but that may only be part of what's missing.

I can confirm that the Tandy GW-BASIC interpreter does not respond to commands in SCREEN 3 (mode 8) and SCREEN 5 (mode 9) because it can't "see" what is typed. Implementing M_TANDY16 in GetPixel(), as in the attached patch, fixes the problem.

With commands being recognized, I noticed that CLS only clears the upper half of the screen in mode 8, but mode 9 is OK. Probably a ScrollWindow() issue with machine=tandy that's similar to machine=pcjr.

Could this thread, or a portion of it, be moved to the patches forum?

Yes, it can 😉

*moved to DOSBox Patches *