PVS-Studio warning V514 for ReactOS

typedef struct _UNICODE_STRING {
  USHORT Length;
  USHORT MaximumLength;
  PWSTR  Buffer;
} UNICODE_STRING, *PUNICODE_STRING;

UNICODE_STRING DosDevices =
  RTL_CONSTANT_STRING(L"\\DosDevices\\");

NTSTATUS CreateNewDriveLetterName(....)
{
  ....
  DriveLetter->Buffer[
    sizeof(DosDevices.Buffer) / sizeof(WCHAR)] =
      (WCHAR)Letter;
  ....
}

This suspicious code was found in ReactOS project by PVS-Studio static code analyzer.
Warning message is:
V514 Dividing sizeof a pointer 'sizeof (DosDevices.Buffer)' by another value. There is a probability of logical error presence. mountmgr.c 164

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/