Short desc:
  page http://en.wikipedia.org/wiki/Image:F-35_gun.ogg can't detect java plugin
 and use it for run java-based player.
  If user manually chooses ( see "more" link under page ) java-based player is to be
  used to play clip all works OK, player applet starts and plays video as expected.

The problem happens on WinVista x64 with IE9 x64 and JRE 6u25 b03 x64.

To compare: in IE 8 x64 java is detected and used automatically.
To compare more: mentioned page works OK on Win7 x86 + IE9 x86 + 6u25 b03 x86 JRE

And more fact( not 100% reproducible ): if we install both x64 and x32 6u25 JRE and try the applet with x32 and x64 browsers it will be working as expected.
  If we remove x32 JRE we'll get non-working x64 JRE plugin autodetection for mentioned page: http://en.wikipedia.org/wiki/Image:F-35_gun.ogg