PVS-Studio warning V567 for saga

bool CLine_Simplification::Simplify(
  CSG_Shape *pLine, int iPart, bool *Keep)
{
  ...
  Keep[iFloater--] = iAnchor == 0 && iFloater ==
    pLine->Get_Point_Count(iPart) - 1;
  ...
}

This suspicious code was found in saga project by PVS-Studio static code analyzer.
Warning message is:
V567 Undefined behavior. The 'iFloater' variable is modified while being used twice between sequence points. shapes_lines line_simplification.cpp 248

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/