Line not visible in code block

Sometimes the code block doesn't show the line where the error occurred.

Here is one example:

This line should be highlighted in the code block. But it's not even visible in the code block: https://github.com/moodle/moodle/blob/89d76fdc25ead41d29253972c45268a21dae7633/lib/classes/message/manager.php#L506

I noticed this in version 2.15. Then I upgraded to 2.18, to see if it was fixed there but the problem persisted.