PVS-Studio warning V511 for samba

#define FSTRING_LEN 256
typedef char fstring[FSTRING_LEN];

char *safe_strcpy(char *dest,const char *src, size_t maxlength)
#define fstrcpy(d,s) safe_strcpy((d),(s),sizeof(fstring)-1)

static bool parse_wbinfo_domain_user(
  const char *domuser, fstring domain, fstring user)
{
  ....
    /* Maybe it was a UPN? */
    if ((p = strchr(domuser, '@')) != NULL) {
      fstrcpy(domain, "");
      fstrcpy(user, domuser);
      return true;
    }
  ....
}

This suspicious code was found in samba project by PVS-Studio static code analyzer.
Warning message is:
V511 The sizeof() operator returns size of the pointer, and not of the array, in 'sizeof ((domain))' expression. wbinfo.c 124

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/