Fire ball in multithreaded example causes window to blank

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In recent testing with svn trunk, I've identified an issue with the 
multithreaded example.

I'm using:
  - Bullet 2.77beta or 2.76 build with double precision.
  - osgBullet rXX built with double precision.
  - Occurs independent of OSG version.

Run the multithreaded example. The cow and a pile of dice appear. Hit return to 
fire a ball into the scene. The window immediately clears to OSG blue and 
nothing else is rendered.

At first, I thought this was an issue with reallocating the TripleBuffer. 
However, I modified multithreaded.cpp to initially allocate the TripleBuffer 
with 32k bytes, in which case firing a ball doesn't cause a reallocation, and 
the issue still occurs. So this is not related to reallocation per se.

There is, however, another issue I've identified with TripleBuffer, which is 
that you can't resize it while running. I'll open this as a separate issue.

Original issue reported on code.google.com by [email protected] on 20 Sep 2010 at 8:30