Safari forcing HTTPS for some HTTP only sites

I have a strange issue with Safari (7.0.1 on Mavericks 10.9.1). It is similar to a few other issues that folk have posted about here but I am opening a separate post because some of the details are different. Please read to the end before suggesting I try disabling extensions, clear cache etc.

This issue is affecting only one user on one Mac (we have several users and several Macs).

We host our own web-site using OS X Server (Mavericks / Server 3.0). Soem areas of the site support both HTTP and HTTPS access. For example:

Live (public) site

http://www.ourdomain.com (on port 80)

https://www.ourdomain.com (on port 443)

and

Test (internal) site

http://www.ourdomain.com:81

https://www.ourdomain.com:444

and

Intranet (internal)

http://www.ourdomain.com:8080

Most areas of the site do not require HTTPS protection and in particular for the Test site both the htp and the https versions have explicit ports. For the Intranet site there is no HTTPS version. For the live and test sites, a certain sub-set of the site requires user authentication and I have redirects setup to redirect access to just those areas via the HTTPS URL which also enforces user authentication.

This setup all works fine, except for this one user on this one machine and only when they use Safari (Chrome and FireFox are fine)...

They have Safari bookmarks saved for the HTTP URLs and after a while:

1. These bookmarks start referring to tthe HTTPS URLs. The actual bookmarks get changed and the http gets changed to https! In the case of the Test and Intranet sites these URLs are not even valid. So, the bookmarks no longer work. If we edit the bookmarks and change them back to http they immediately revert back to https!

2. If one types the HTTP URL directly into the address bar then Safari ignores the HTTP and instead tries to go to the HTTPS version of the URL.

Basically, there is no way to get Safari to access the HTTP versions of any of these URLs with the resuklt that the Test and Intranet sites are unusable.

This user only has the same extensions as other users have and they all work okay. We have tried disabling extensions but it does not resolve the issue. Doing a full reset of Safari will resolve the issue temporarily but this deletes a lot of stuff, such as History, that the user does not want deleted. And the issue always recurs after a while anyway.

Does anyone have any idea what is causing this behaviour and how to prevent it? It is driving me and the affected user mad!