PVS-Studio warning V599 for Virtualdub

class VDDialogBaseW32 {
  ....
  ~VDDialogBaseW32();
  ....
  virtual INT_PTR DlgProc(....) = 0;
  virtual bool PreNCDestroy();
  ....
}

class VDDialogAudioFilterFormatConvConfig :
  public VDDialogBaseW32
{ .... };

INT_PTR CALLBACK VDDialogBaseW32::StaticDlgProc(....) {
  VDDialogBaseW32 *pThis =
    (VDDialogBaseW32 *)GetWindowLongPtr(hwnd, DWLP_USER);
  ....
  delete pThis;
  ....
}

This suspicious code was found in Virtualdub project by PVS-Studio static code analyzer.
Warning message is:
V599 The destructor was not declared as a virtual one, although the 'VDDialogBaseW32' class contains virtual functions. VirtualDub gui.cpp 997

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/