menu from subsites link to main site

WP 3.1.3 multisite, Domain Mapping 3.0.4, other plugins include marketpress, membership.

Permalinks set to Day and Name.

head site is which has some pages and a custom menu.
subsite 1 is which also has pages and a custom menu.
subsite 2, 3, 4 ditto

The problem is that the links from the menu on subsite 1 etc all say they are linking to etc but in fact try to load the main page of

Is this a permalinks issue?

Or do I need some other menu manager?