PVS-Studio warning V519 for Clang

std::string ASTContext::getObjCEncodingForBlock(....) const {
  ...
  ParmOffset = PtrSize;
  // Argument types.
  ParmOffset = PtrSize;
  ...
}

This suspicious code was found in Clang project by PVS-Studio static code analyzer.
Warning message is:
V519 The 'ParmOffset' variable is assigned values twice successively. Perhaps this is a mistake. Check lines: 3953, 3956. clangAST astcontext.cpp 3956

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/