fcaps.eclass is using group name 'root' which is not available on BSD system. Instead you can use "0", or $(id -g -n 0) if you'd prefer "group name"
Index: fcaps.eclass
===================================================================
RCS file: /var/cvsroot/gentoo-x86/eclass/fcaps.eclass,v
retrieving revision 1.8
diff -u -r1.8 fcaps.eclass
--- fcaps.eclass 27 Jun 2013 01:18:57 -0000 1.8
+++ fcaps.eclass 13 Apr 2014 00:16:44 -0000
@@ -80,7 +80,7 @@
# Process the user options first.
local owner='root'
- local group='root'
+ local group=$(id -g -n 0)
local mode='4711'
local caps_mode='711'
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