sipXconfig attempts to calculate appropriate Search Base when connecting to LDAP server. However it's done only when setting up the first server.
If search base is already configured sipXconfig will not overwrite it, because it suspects that user might have changed it manually.
It is causing problems when switching to LDAP server with a different tree, the search base is incorrect and preview falls. XCF-1832 makes things even more difficult because Internal Exception is displayed instead of the standard error message.