PVS-Studio warning V541 for TinyCAD

void CChildFrame::OnUpdateFrameTitle(BOOL bAddToTitle)
{
  ....
  CString csText;
  ....
  if (m_nWindow > 0)
    csText.Format(_T("%s: %d"), csText, m_nWindow);
  ....
}

This suspicious code was found in TinyCAD project by PVS-Studio static code analyzer.
Warning message is:
V541 It is dangerous to print the string 'csText' into itself. childfrm.cpp 79

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/