ImageIO.write does not write content to file on Solaris and Linux

When writing images using ImageIO we are seeing odd results.
I have a test case which I was running with 1.6.0_20.
The test creates a JFrame, builds a BufferedImage from it, and then saves it as a ‘png’ and a ‘jpg’ file. When the test is executed on Windows the images are saved and viewable as expected.
When executed on Linux x64, Solaris x86 (and other UNIX platforms as well) using the 1.6.0_20 32-bit JRE, when I view the saved images I only see a black canvas.
Another data point, if I run the same test with Java 5 on UNIX the images are written correctly
to the ‘png’ and ‘jpg’ files.

It seems to be something with Java 6 and UNIX specifically.