If you have relative URLs in your templates or content, open eZ Studio and click in one of those links, the eZ Studio URL will get messed and you will have 404.

Steps to reproduce

Assuming your site is hosted in http:// 1-5.ez and you have three siteaccess: site, some_and _other.

• In one of you templates or content, add a link to the other siteaccess (a navigation menu, for example):

  <a href="other">Other</a>

• Create a landing page Mypage and add dynamic content to it.
• Open the landing page in eZ Studio:
  http://1-5.ez/ez#/studio/insite/%2Fsite%2FMypage
• Click on the link that will appear in the content area. The URL will change
  http://1-5.ez/ez#/studio/insite/%2Fsite%2FOther

You will get a 404