According to

http://download-llnw.oracle.com/javase/6/docs/technotes/guides/plugin/developer_guide/debugger.html#jpitf

"The Java Plug-in trace file records all the debug, System.out, and System.err messages. The trace file [...] is automatically enabled when the Java Console is enabled."

This is true for Java 5, but it is not true for Java 6 (including 6u21).
It is reproducible even with the first public JRE 6.

How to reproduce:
- Open the Java Control Panel
- Select the Advanced Tab
- Uncheck Debugging/Enable tracing
- Uncheck Debugging/Enable logging
- Uncheck Show applet lifecycle exceptions
- Check Java console/Show console
- Open IE or Firefox
- Open any Applet
- If you use Java 6, you can notice that a trace file is NOT written
- If you use Java 5, you can notice that a trace file is written