I'm not completely surethat I actually switched from fping to hobbitping, though, because I'm still seeing fping-std* files in server/tmp (as a result of "CMD bbtest-net --report --ping --checkresponse --debug" in hobbitlaunch.cfg.).
Those filenames are built into the bbtest-net utility. I've changed them for the 4.2 version, but you're probably still running the 4.1.2p1 version of bbtest-net.