sigwait return 4

[Slawa Olhovchenkov]

System is 8.2-RELEASE (GENERIC), amd64.
Application -- i386 for freebsd7.

In ktrace dump I find some strange result:

 22951 100556 kas-milter CALL  sigwait(0xffdfdf80,0xffdfdf7c)
 22951 100556 kas-milter RET   sigwait 4
 22951 100556 kas-milter PSIG  SIGUSR2 caught handler=0x804c0f0 mask=0x4003 code=0x0

RET   sigwait 4 confused me, and, I think, confused application too.

man sigwait:

ERRORS
     The sigwait() system call will fail if:

     [EINVAL]           The set argument specifies one or more invalid signal
                        numbers.

     [EFAULT]           Any arguments point outside the allocated address
                        space or there is a memory protection fault.


How sigwait can return '4'?
May be EINTR, converted from ERESTART? But kern_sigtimedwait from sigwait must 
be called with timeout == NULL...