I've defined a custom property that was only being populated when viewed in Edit mode, I have now narrowed it down to an issue with languages.

I've created a page template called Test.aspx, if I navigate to it using the URL mysite.com/Templates/Pages/Test.aspx?id=141 then everything works fine, the custom properties are populated with data.

However, when I navigate to mysite.com/Test-Page (which is what the above url is re-written to), the custom property values are not populated.

If I view the page in edit mode then again the values are populated, however when I use the View Mode button the values are missing. I think this might have something to do with edit mode having the cookie editlanguagebranch, as mentioned in this globalization article: http://sdk.episerver.com/library/cms6/Developers%20Guide/Core%20Features/Language%20Settings.htm

In our site the only language I have switched on is English UK. I have then performed the following tasks to ensure only this language is used:

• In web.config set <globalization culture="en" uiCulture="en-GB" requestEncoding="utf-8" responseEncoding="utf-8" resourceProviderFactoryType="EPiServer.Resources.XmlResourceProviderFactory, EPiServer"/>
• In EPiServerFramework.config set <add name="mysite.com" language="en-GB" /> and then <add name="*" language="en-GB"/>
• Added a new cookie epslanguage, with value set to en-GB
• In every file in the /lang folder, changed <language name="English" id="en"> to <language name="English UK" id="en-GB">

Is there anything I've missed here? 

Any help is much appreciated