I think there are some stuff you can do:
Try yhkwongs SVN build or any SVN build
Try different output in the dosbox config
And/or set sdl to use windib or not use windib (do a search here for windib for instruction).
If any of this works, please donate $2 to the dosbox devs 😉

I am not certain of the exact cause of the problem, but you may find some guidance here:
dosbox keyboard problem

Thanks Dominus. Some of that is over my head. What do you mean by
'try different output'. I will try the windib change. I'm willing to donate much more than $2 for a specific
fix.

Thanks ripsaw, but that thread mostly lists a lot of voodoo with no specific fix. Lacking a better
answer, I guess I'll try the voodoo.

I guess you are on Windows, then the installer added a shortcut to your startmenu (in a dosbox folder) called "edit config" or similar (it's been a while since I was using Windows). Click that and your dosbox config will be editable with notepad. You will notice several groups of settings, in the first obe you can find the output setting and a bit higher up the possible values

OK, I permuted through all the output options (surface, opengl, openglnb,overlay) (why would output options affect keyboard input??) ) - no change.
I tried SET SDL_VIDEODRIVER=WINDIB (though I was unclear where, so I tried in the config file and in the Xp cmd prompt)
Also tried SET SDL_NO_RAWKBD as above. in config file no help. In cmd prompt, errored as undefined, so I tried
SET SDL_NO_RAWKBD=TRUE and =FALSE, but no change.

Please forget your proposal of a $2 donation. I will happily pay $100 donation/fee for a proper precise fix.

thanks,
tom

When you set some sdl stuff on the cmd prompt (which is the way to go to test stuff, to permanently set this you'd use some Windows setting), you will have to start dosbox from that prompt as well. If you did this, then I'm out of ideas.

A precise fix for a problem requires the precise cause to be known.

That said, does this repeating key problem happen in DOSBox's shell, or does it only happen after booting into MS-DOS 6?

Dominus: yes, I started dosbox from the same command prompt in which I had set the variables.

Ripsaw: while the original hardware and disk boots dos6 then runs the app, under dosbox i simply mounted a copy
of the original drive as C in dosbox, then ran the app. (dos6 files are there, but it's not clear they are ever touched.)
Dosbox seems to provide a 'DOS' natively. So i'd say the repeating appears in the dosbox shell. Is there a way I should run my copy of dos 6 within dosbox? How would this work?
seems like dosbox config leaves off at launching an autoexec (if configured), not booting an OS. What does it mean to run dos6 within dosbox?
The native PC hardware running dos6 doesn't have this problem - I don't know if it's a difference in the emulated BIOS
or emulated DOS. If the latter, maybe booting dos6 will fix it. How do I boot a dos6 within dosbox?

thanks again,
tom

See boot command 😀