mbstring.func_overload and PHP Warning

Hello, so I’d like to get some confirmation on something.

I recently migrated a bunch of existing WordPress installs to a new host. The new host I setup fully modern, which included latest PHP (5.4.16) and all the typical default configuration that I would do.

This included setting mbstring.func_overload = 7 — so that all UTF-8 was properly handled.

However, immediately after migration, my error log started filling with these errors:

[12-Jun-2013 19:41:02 UTC] PHP Warning:  mb_stripos(): Empty delimiter in /[....]/wp-includes/functions.php on line 658
[12-Jun-2013 19:41:02 UTC] PHP Warning:  mb_stripos(): Empty delimiter in /[....]/wp-includes/functions.php on line 661

After doing a bit of searching, I ran into this old thread:
https://www.ads-software.com/support/topic/php-warning-mb_stripos-empty-delimiter-caused-by-wp-cronphp?replies=19

Thing is … from reading that thread, and from playing around. I realized that the mbstring.func_overload seemed to be the issue. I checked and the old server, in fact, had it set to 0

I changed mine on the new server to 0 … and it INSTANTLY stopped having issues.

But now that begs a new question:

“Can this be right?”. I would assume (especially after hearing Nacin speak at php[tek] 2013, in his keynote, about how WordPress is designed to just ‘always work, no matter what the PHP config) …

I would assume that WordPress would work fine whether mbstring was on, or off.

I personally don’t want mbstring turned off, because I have other scripts/websites on that server that should have the mbstring on.

So this is truly a bug in WordPress now that should be filed? That it should work correctly regardless of whether func_overload is on?