This affects all versions of JIRA - client comes along and posts a whopping great big chunk of something in to a code panel that results in the panel invariably becoming very wide making the whole page super-wide and you have to horizontally scroll just to find links and buttons, etc. Truly painful.

Very easy fix - add this CSS:

div.codeContent {
 overflow: scroll;
}

You can see it in action in some of the code panels here: http://jira.adaptavist.com/browse/BUILDER-722

With scrolling code panels, it's soooo much easier to work with JIRA.