Thread:Project:Support desk/Fatal error: Maximum execution time of XX seconds exceeded in includes/StringUtils.php on line 323

I'm getting this error on a page which uses a custom extension tag. I know I can fix it by upping the execution time, reducing the size of the page, etc. What I'm curious is why does it always fail on that line? If you search Google for StringUtils on line 323, you will see the same error message on tons of wikis out there. Line 323 looks like this:

$result = strtr( $subject, $this->data );

Is there some specific type of input that is causing the page to die on that line?