ZDoom

As of 35186e9fd722.
This looks a bit like the problem here, but this time affecting the standard menu.
As you may see, some of the glyphs on some of the lines are clipped.
There might be a pattern to it, but it must be a quirky one - it doesn't depend on the glyphs, as they're rendered correctly in other places of the same menu, neither does it seem to depend on glyph color.

What screen resolution, scale factor and scaling mode are you using?

I doubt resolution matters - it happens both widowed and fullscreen.
It seems to be set to 800x600 though.

I use either hqnx or xbrz - problem visible with both.
User interface scale set to 2.

If you were referring to something else, say so clearly.

Graf is referring to your GZDoom resolution (regardless of whether it is windowed or fullscreen), the “Resolution scale” and “Scale factor” settings in GZDoom, all found in Options > “Set video mode”.

Was this really 800 x 600?
There was a problem causing a glitch like this when the window was dragged to its minimum size. The handler allowed a minimum WINDOW size of 640 instead of a minimum CLIENT size and if that happened the problem described here happened - it was also the only case where I could reproduce it, and that part is already fixed.

If this is Linux, though, I cannot say. If this is the case there may be a problem in the backend code reporting wrong window sizes.

There is currently an issue in Windows where the client size can be arbitrarily set (vid_setsize) to a small size - however the scaling code handles this by forcing the scaling to be 640x400 minimum no matter what the window size is.

I fixed that issue yesterday. The limit was 640x400 window size, not 640x400 client size.

Let's put it this way: ...and yes, it's Linux.

Also, for comparison (as of 6d1a85af3c5a5f6):
...so it seems distortions happen at a certain height...

Is there any bug here?
To me, this seems like the usual issue of Nearest Neighbour filtering crapping itself when non-integer values (be it scaling or coordinates) are introduced.

It shouldn't do any non-integer scaling in the menu, unless the height is less than 480.

I'm incapable of reproducing this on my end. This is really odd. What window manager / desktop environment do you use?

...I rarely visit this forum these days.

As for my window manager, it's openbox.
DE doesn't really count, as it's actually a collection of bits and pieces (lxpanel, pcmanfm, etc.).

Also, still valid as of dc3b36ebd.

Whatever this is, I strongly suspect a third party related problem.