PVS-Studio warning V519 for QT

bool qt_testCollision(const Q3CanvasSprite* s1,
                      const Q3CanvasSprite* s2)
{
  ...
  t=x1; x1=x2; x2=t;
  t=y1; x1=y2; y2=t;
  ...
}

This is what should have been written here: t=y1; y1=y2; y2=t;

This suspicious code was found in QT project by PVS-Studio static code analyzer.
Warning message is:
V519 The 'x1' variable is assigned values twice successively. Perhaps this is a mistake. Check lines: 2218, 2219. Qt3Support q3canvas.cpp 2219

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/