Creating a web check step with a very long post causes this error to get thrown when clicking on that step to modify it. The cause seems to be that when popup_httpstep.php is called, it passes in all of the field values as part of the query string instead of reading those values from the database when popup_httpstep.php is loaded, causing extremely long URLs to be generated anytime the post or header fields contain a large amount of data.

Unfortunately, the monitor we have to put in has a post of around 50k characters and appending that to a URL is just not feasible. The result is that large items like this cannot be modified in the Zabbix frontend after they are created unless we set Apache's LimitRequestLine setting to 100000 or more.