3nov15
The following is form Sherwood's documentation and may shed light on 
our versionitis problems.

iVPython 6 is based on the cross-platform library wxPython (wxpython.org), which allows Python programs to create windows and handle events on Windows, Macintosh, and Linux. The major changes from VPython 5 made possible by wxPython are the elimination of nearly all platform--dependent C++ code, the elimination of complex multithreading in the C++ code, and the ability for Macintosh versions to use 64-bit Python based on the Cocoa framework (VPython 5 on the Mac was based on the Carbon framework, which is no longer supported by Apple).

Almost all VPython 5 programs will run on VPython 6 with no change. However, animation loops must have a rate or sleep statement (not time.sleep) to permit the screen to be updated, and you must import visual or vis before importing graph or controls or filedialog, which most users have always done anyway.

 
1nov15
Somewhat obscure ... does not reveal easily just how the 
mouse event cue works in visual.py. 

Versionitis:
Sadly, visual suffers from versionitis in that nice, simple examples
that worked in earlier years wont work in later years, and version
number for the example itself, or the error messages revealing the 
version incompatibility is absent. 

So using older sample programs is dicey and disappointing.