In Windows Terminal 0.11.1251.0, a new VT attributes bug has been introduced.

When output contains VT escape sequences to set text attributes, they are sometimes ignored when the cells contains the space character.

If this sounds a lot like #5502, it is because it's probably exactly the same issue, you need to write spaces not only when the background color is different, but also if some other attributes, such underline are set (and you probably should make sure you include reverse video and crossed-out as well).

Repro command line : curl 'https://raw.githubusercontent.com/PhMajerus/ANSI-art/master/Windows%20Terminal.ans' | sed 'H;$!d;x;s/\x1A.*$//' | iconv -f CP437

Compare the top of the "W" with conhost:

It seems to be a bit random, even when it's not scrolling the buffer:

File used: https://github.com/PhMajerus/ANSI-art/blob/master/Windows%20Terminal.ans