This applet intermittently load problem is Java Plugin specific. It's related to mismatch of plugin instance to be destroyed when the applet destroy request (triggered by page refresh) is received too late -- after a new plugin instance has already been created. When that happens, instead of destroying the old plugin instance of the previously loaded applet, the newly created instance is disposed, preventing any LiveConnect or communication between the browser and the applet, and therefore, preventing the JS->J call to load the StarOffice encoded document.
This problem is in JPI code all along but the changes from 1.5 to 1.6 (and beyond) probably made the problem surface more easily now than compared to running with 1.5.
Fix is understood. Will get fix in to both 7.0 and 6u2.