OK I figured it out: I needed to say "enable vga resize delay" to true and it fixes it.

Just a gentle reminder that Daum is no longer maintained by the original guy and nobody has picked up where he left off. At this stage, it is well behind mainline DOSBox.

In short:

• A lot of the bugs in Daum are unique or have been fixed by mainline DOSBox.
• Daum is different enough from current mainline that the DOSBox devs won't be able to help you.
• The original dev doesn't work on Daum anymore, so he won't be able to patch it for you.
• I'm not aware of anyone else who can either.

If you can do without the Daum exclusive features, you'll have a big advantage in using an up to date release of either mainline DOSBox or one of the currently maintained branches.

I'd be happy to if they'd just add MT-32 emulation in mainline DOSBox. I've asked for this on multiple occasions and think it's ridiculous they won't do it. They wouldn't even have to bundle the copyrighted ROM, just make it possible to drop it in.

Plus if you want Munt just use ECE DOSBox. Even standard DOSBox works with stand alone Munt.

It's easy to say something is ridiculous if it isn't your head on the chopping block... snd yeah, installing Munt and using this is a no-brainer. And Munt has evolved so much that the build in on Daum is not something you should mention 😉

Using Munt standalone and wiring it up is a total pain in the ass. I want it built in to DOSBox.

Then you must have a Roland MT-32 so why do you want it built into DOSBox? Unless you don't want to cart around the MT-32 with you of course.

Erm, yeah, I don't want to cart it around with me. Or wire it up when I have a whole DOS PC emulator. For that matter, why use DOSBox at all instead of a full-on old PC? 😀

Anyway I tried out the ECE and it does builtin MT-32 emulation nicely. Thanks for the advice @collector.

Good! YP80 is maintainer for this branch. He's a cool guy and he's on this forum, so he'll be able to help you if you find any bugs in the ECE build.
DOSBox ECE (for Windows & Linux)

Even though you are good with ECE, what do you mean with munt and wiring it up being a pain in the ass? Maybe I'm missing something, but you just need to install Munt, point it at the roms and then point Dosbox at Munt

I seem to recall it being a pain last time I tried it. In Windows 10 Microsoft have removed all MIDI configuration from the GUI. It's just much easier having it built in.

Hmm, it's just a matter of pointing Dosbox at the right midi port. I think it tells you which is which in the console.

mixer /listmidi
0 Microsoft GS Wavetable Synth
1 MT-32 Synth Emulator

=> dosbox.conf
midiconfig=1

But yes, changing the default MIDI device has no built-in GUI option in Windows 10.