Double left border on focused Input?

[serddmitry]

I'm adding a few simple Inputs with default margin 0.
When an Input is focused - there is a weird double border on the left, see screenshot.
If I set non-zero margin on the Input - the border looks correct (single left border, just like on all other sides of the Input).

What is this? Is this expected? How to have simple single border with zero margin?
I'm on MacOS. The issue seems unaffected by selected terminal font and terminal app.
Using textual 8.0.2.

Thank you!

[serddmitry]

This behavior is specific to border "tall".

[TomJGooding]

Are you using iTerm2? Could you check whether this is disabled: Settings > Advanced > Extend background color into margins in alternate screen mode?

[serddmitry]

Yes, unticking this feature does indeed remove the artifact, thanks for the hint!