Extended Memory Size has no effect

Hi There,

We have a client who pushes to the memory size limit. We temporarily extended the limit and it shows in the dashboard but we still get the following error message in our log file:

PHP Fatal error: Allowed memory size of 157286400 bytes exhausted (tried to allocate 154839 bytes) in /.../wp-includes/functions.php on line 316

What can we do?

Another question: Is it possible to extend the memory size for a single site?
Last question: The Limit was set to 2GB. Why is the memory size exhausted with 157286400 bytes?

Thanks, Tee