Like everything if you RTFM it works as described. If you are coding PHP you would know this behaviour.
I disagree that most or even many PHP programmers know this issue. A few months ago I demo'ed an exploit in code that a coworker wrote which had the same flaw, this time in comparing MD5 hashes. He had been using PHP for all of his professional career and had no idea how PHP compares strings with leading digits.
Of course, I only knew about the issue because of a similar bug that I wrote, sometime a bit over a decade ago. At that time I had been using PHP for over five years.
So the maxim "know your tools" still stands, but string comparison in PHP _is_ broken in subtle, dangerous ways that most devs will never (knowingly) encounter. I've never seen code that _relies_ on this behaviour, I would love to see it fixed in a major version release. Too bad PHP 7 still carries this flaw.