Use with ImageMagick v6.9.x causes opacity to be ignored

[Cride5]

Rendering is known to work properly using:
ImageMagick 6.7.7-10

And is know to fail to render opacity correctly using:
ImageMagick 6.9.3-0

Various attempts have been made to fix this, including specifying options like:

• -alpha set
• -channel RGBA
• -define png:format=png32
  and by using "fill-opacity=0.x" rather than just "opacity=0.x"

None of the above has worked. Any suggestions that might fix this welcome..