Highlight current line option makes text blink on and off

If I use the “highlight current line” option in the preferences, I find that inserting the cursor inside a line of text will make another line of text (either the one above or the one below it) blink on and off; that is, that affected line of text will disappear for a fraction of a second and then reappear.

This is a minor annoyance but one that is sufficient to force me to turn the option off.

Is this a known issue?

That doesn’t ring any bells for me specifically, however the highlight line feature (along with block cursor) do both introduce a bit of complexity into the equation that can interact poorly with other options or conditions (we’ve fixed a number of them over the years). Under normal circumstances you shouldn’t be seeing anything like you describe, in other words. What I would do is try changing settings here and there to see if anything impacts the behaviour. Block cursor is definitely one to look at, anything that changes the shape and content of the editor (like fixed width or page view or line numbering), the appearance of the text (like zoom levels or invisible characters) or even the text formatting might be of impact. See if text using very basic 12pt text at 1.0 line height (and no other paragraph spacing) exhibits the same issues.

One quick way to confirm whether there are any preference conflicts is to save your current preferences to a preset with the Manage… button along the bottom of the preference pane, and then click the Defaults button to the right and confirm. Now try turning line highlights back on and see if the odd behaviour has vanished. If it has, try applying your preset and see if it returns.

I had the preference “Use block insertion point of [N] pixels” enabled.

Disabling that made the problem go away.