PVS-Studio warning V501 for TPP

void DIGEST_PROTEIN(char *szSeq,
       int iLenSeq)
{
  ...
  if (pOptions.bMarkNXST
      && szPeptide[i] == 'N'
      && szPeptide[i + 1] != 'P'
      && (szPeptide[i + 2] == 'S' ||
          szPeptide[i + 2] == 'T')
      && szPeptide[i + 1] != 'P')
  ...
}

The index in the last line should be this: [i + 3].

This suspicious code was found in TPP project by PVS-Studio static code analyzer.
Warning message is:
V501 There are identical sub-expressions 'szPeptide[i + 1] != 'P'' to the left and to the right of the '&&' operator. Comet_fastadb comet-fastadb1.cxx 1906

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/