fping finally seems to be picked up by a new maintainer - which is great (see http://fping.org/ )
the problem is that zabbix source ip detection breaks with fping3.
zabbix tries to detect whether fping help output contains -I or -S flag (in that order), and uses that option with the source ip specified.
unfortunately for zabbix, fping3 uses -I for source interface, and -I comes first in the fping3 help output, so zabbix picks it up and uses -I<sourceip>, which fails and makes fping3 to ignore this parameter
this is true for both fping 3.0 and 3.1-rc1 (both already used in gentoo)