refClockSyncCycles="-1", I got Messages.

I found lot of messages
"Failed to get reference clock time: Input/output error"
in LinuxCNC Console 
when I set "refClockSyncCycles="-1" to EtherCat Master configuration.

But if I set refClockSyncCycles="1", I could not see such messages.
I attached
refClockSyncCyclesMinus1.linuxcnc.txt (LinuxCNC Console Log)
refClockSyncCyclesMinus1.dmesg.txt (dmesg Log)
when I execute with  "refClockSyncCycles="-1"

And also, for reference, I attached 
refClockSyncCycles1.linuxcnc.txt (LinuxCNC Console Log)
refClockSyncCycles1.dmesg.txt (dmesg Log)
when I execute with  "refClockSyncCycles="1"
 

github.com/linuxcnc-ethercat/linuxcnc-ethercat/pull/461

There is a bug in the linuxcnc-erhercat if you just set the negative option