java version "1.3.0beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0beta-b06)
Java HotSpot(TM) Client VM (build 1.3.0beta-b04, mixed mode)

Tested with Redhat Linux 6.1, 6.1 update and 6.2.
Alt+mnemonic can not work.
This function worked fine with jdk1.2.2.

Reproduce to:
1,Run (DEMO) SwingSet2.
2,Select menu like this, ALT+F(File) or ALT+L(Look&Feel) or ALT+T(Themes).
3,menu does not open.