Hi,
I have two sites and two user groups, one for each site. I have customised the Asset Map Root Asset for one of the user groups only while the other group will see the usual default assets in the asset map (trash, designs, etc.).
All good.
Now I have a user linked in both user groups and when they login to the admin interface for either site, they always see the customised root asset only. They can click on the "restore root folder" icon to get the default map to appear but I cant figure out how to set it up so they see the two different maps when they log in to site A or site B.
thanks for your help 
The admin interface is the same for both sites. The URL just tells Matrix where to auto-expand the asset map to. You can only set one asset map root node per user.
If you have two set, like in your case, Matrix will find a common parent and use that as the root node. In your case, one group asks Matrix to display the top level, so that is what Matrix is using as it needs to display all assets to this user.
But I have set only one custom root node (for users in group B editing site B, which auto-expands to show just one specific section of site B ). Users in group A don't have a root node set and use the global preference (which is the default blank setting).
So just to confirm that I've got this right, it doesn't matter if the linked user accesses siteA.com/_admin or siteB.com/_admin because the group B custom root node takes precedence over the global preference setting used by group A and so the user will always see group B's custom root node?
I just assumed that if the linked user accessed siteA.com/_admin, they'd see group A's normal version of the asset map and if they accessed siteB.com/_admin they'd see the auto-expanded version… :unsure: