Something similar happens with many ISA cards - with ET4000 at resolutions that use the 25MHz pixel clock (320x200, 640x400) when using a flat screen monitor. Doesn't happen on a CRT.
Haven't found the cause or a workaround yet. It almost looks as if some oscillation is building up in the cable.

This happens on many graphic cards. One of my Cirrus Logic had really bad "effect" on LCD monitor. But nothing on CRT.

Yup....
Seen that on my ISA cards too. (ET-4000-ISA, Trident-9000-ISA and ET-3000-ISA)
I have ordered a VGA splitter-box that according the manufactor can boost the signal.
I really do not know if it can force the TFT to display stuff differently.

Anyway...
I too have problems as said. And I have seen it on aprox 50% of all the games
that I have tried on MS-Dos-6.22.

Ah, so nothing wrong with the card?

Probably not. If you have no issues in Lemmings-1 and issues in Lotus Ultimate Challenge plus Civ-1, it's just how TFT's display that resolution.

brostenen wrote:

Probably not. If you have no issues in Lemmings-1 and issues in Lotus Ultimate Challenge plus Civ-1, it's just how TFT's display that resolution.

Don't have Lemmings 😜

Try search, if there were ever a shareware-ish kind of demo something release....

EDIT:
If this is not the shareware version, then I will remove the link again.

http://www.dosgamesarchive.com/download/lemmings/

Works fine when selecting "compatibility." No lines or anything, but the icons showing the actions don't show. And choosing PC compatible gives me a black screen at starting the game from the main menu.

Ahh... Why exactly this, I do not know.
The ISA cards that I have tested Lemmings on, were all installed in both a 386 and a 486.
Running MS-Dos-6.22 and not Win9x. Some times it is Win that makes issues too.
Unless some settings are made. You know how it is. 😁

As long as you do not get any of those vertical lines, you know the card is good. 😀
And the issue is the monitor being slightly incompatible with the card.
Nothing that serious, that it will prevent you from using it, only minor irritating issues.

brostenen wrote:

Ahh... Why exactly this, I do not know. The ISA cards that I have tested Lemmings on, were all installed in both a 386 and a 486 […]
Show full quote

Ahh... Why exactly this, I do not know.
The ISA cards that I have tested Lemmings on, were all installed in both a 386 and a 486.
Running MS-Dos-6.22 and not Win9x. Some times it is Win that makes issues too.
Unless some settings are made. You know how it is. 😁

As long as you do not get any of those vertical lines, you know the card is good. 😀
And the issue is the monitor being slightly incompatible with the card.
Nothing that serious, that it will prevent you from using it, only minor irritating issues.

I actually just googled "Lemmings MS-DOS" and downloaded it from the first link (probably not legal, not advising anyone to do so) and that worked perfectly, so it was just an issue with the shareware version 😜

Legallity can be disputed.... I don't know if it is considered abandonware or anything. 😉
At least you can delete the download now, well knowing that the card is working. 😜

I got the same issue with lots of cards, always thought it was normal:
Trident 8900D, 9000i-3 (2 cards)
Cirrus Logic GD5420, GD5428
WD Paradise PVGA1A

However, they are all ISA and my PCI never had this issue.