Cable Test Fail (Monitoring-->Ports-->Cable Test)

I have (3) S3300 switches stacked. all have same (Latest) Firmware and stack works well. Switch #3 shows port #28 to be open at 28 meters. If I do a cable test (Monitoring-->Ports-->Cable Test) on that port, it says cable test failed and the IP Phone attached will not work until I reboot the switch. There are several ports on this switch that exhibit the same results. Using cable testing equipment all ports show that the witing is correct. Normally I would not consider a cable test failure a problem but since there are 5 ports on this switch that have the same issue and the IP phones stop working if I do a cable test from the switch untilI reboot the switch. Any ideas?