We had a problem with jumpstart/NFS setup; perhaps similar to yours? It was related to non-standard net masks (i.e. 192.168.0.0/255.255.252.0 is not class-C). While DHCP provided the correct options and parts of the installer loaded ok, then it reset the networking settings to "correct" ones per network's class (snoop showed that broadcasts went to 192.168.1.255 instead of 192.168.3.255, etc).
While this problem was googled as valid for old releases, we were surprised to trigger in Solaris 10u4 (8/07). A working solution was to separate the setup/mgmt network to a correctly classed one (i.e. 192.168.16.0/24) on a separate interface (with individual MAC address for DHCP/TFTP purposes). This message posted from opensolaris.org
