I had the same problem and saving the jpdl files certainly produces a png file for me.
Not a very interesting one though. It always has a diagonal line from the top left extending about a fifth of the way down the image.
Nothing else.
This is a freshly installed download of 4.4. I'm running JBoss 5.1.0.GA, though this is before the images get near that. Note that I can see images when I open the jpdl inside eclipse. So my sequence is:
1) open jbpl with plugin in eclipse.
2) note the image ... looks okay
3) save the jpdl, note that the png is created
4) view the png and note that is just a diagonal line as described above.
My desktop is Ubuntu, 10.04 and I am running Eclipse Galileo downloaded especiall for this, so no extra plugins are installed in Eclipse.
Any idea what is wrong?