mild annoyance: periodic empty haystack errors

Hello, this is my first post to the wp support forum.

I’m having a periodic issue on my wordpress blog. On entries that include pictures, the following error message gets repeated a number of times:

Warning: mb_strstr() [function.mb-strstr]: Empty haystack in /home/vecsluo7/public_html/wp-includes/functions-formatting.php on line 45″

This error surfaces according to seemingly no rhyme or reason. If I reload the page in my browser, magically the error disappears. Sometimes this error message takes a few reloads before it goes away. And other times, it does not appear on my blog for a few days.

My blog address is http://jamesluong.com Does anyone know how to resolve this?

Thanks.

James