This has been written about several times by other people with no real satisfactory answer. I'll try my best to layout the problem as succintly as possible.

I have two sites managed by the same Umbraco instance. So below the Content node there are two top level nodes (called egtb and afc respectively) each having it's own hostname. For reference the sites are:

egtb.capbuild.com
afc.capbuild.com

I want the site editors to be able to link content between the two sites using Content Picker. So for example the home page of egtb.capbuild.com should have a link to afc.capbuild.com. It should not link to a url within it's own domain. I am getting inconsistent results though, on some pages the correct hostname is applied when linking to a page on the opposite domain, but sometimes umbraco is trying to use the current host name.

See homepage of http://afc.capbuild.com/ for a particular inconsistent example.
* The link "Link to Airfield Data" is correctly linking across to egtb.capbuild.com
* However, the link "Link to the AAA Engineering" is currently linking to http://afc.capbuild.com/airfield-facilities/engineering-and-avionics/aaa-engineering.aspx whereas is should link to http://egtb.capbuild.com/airfield-facilities/engineering-and-avionics/aaa-engineering.aspx

This problem appears to affect only pages Level >= 3, pages with Level = 1 or 2 seem to work as expected.

Note that the Properties Tab of pages with Level 1 or 2 show the following:
[code]Link to document http://egtb.capbuild.com/flying-into-wap.aspx
Alternative Links http://egtb.capbuild.com/flying-into-wap.aspx[/code]

Whereas the Properties Tab of pages with level >= 3 shows the following:
[code]Link to document /airfield-facilities/engineering-and-avionics.aspx
Alternative Links http://egtb.capbuild.com/airfield-facilities/engineering-and-avionics.aspx[/code]

This was manifesting itself in v4.0.0 so I've spent the morning upgrading to 4.0.1 and the issue remains.

I have set the following:
Umbracosettings.config:
[code]
[/code]

web.config
[code]
[/code]

I've also republished the top level nodes and all their children.
I've also removed the hostnames from both top level nodes, added them again and republished. All to no avail.

Please help, I want to go live in a few days!