PVS-Studio warning V568 for ReactOS

static DWORD CALLBACK
RegistrationProc(LPVOID Parameter)
{
  ...
  if (0 == LoadStringW(hDllInstance, IDS_UNKNOWN_ERROR,
          UnknownError,
          sizeof(UnknownError) / sizeof(UnknownError[0] -
          20)))
  ...
}

A parenthesis seems to be put in a wrong place. This code should look like this: sizeof(UnknownError) / sizeof(UnknownError[0]).

This suspicious code was found in ReactOS project by PVS-Studio static code analyzer.
Warning message is:
V568 It's odd that the argument of sizeof() operator is the 'UnknownError [0] - 20' expression. syssetup wizard.c 1696

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/