Recent example:
https://build.golang.org/log/840ef7221cf0147181be16e21a553166c3a9c546

(or click any of the many red buttons in the darwin columns at https://build.golang.org/?repo=golang.org%2fx%2ftools#short :( )

This feature is os-dependent, so it would not be surprising if this is a real bug. Unfortunately, I ran it on gomote and was not able to repro after dozens of attempts. @stamblerre also ran it locally on darwin 1000x and was not able to repro.

CC @heschik