Drag-n-Drop operation is not working on applets which are running older versions of JREs(prior to 6u10) on top of OOPP plug-in. One can drag out such applets, if they are requesting a insecure version of JRE , by clicking on the "Cancel" button of SSV related security pop-up since in that case applet will actually get launched using 6u10.
If applet is requesting or loaded using secured version of JRE from the previous train then there is no workaround available to drag them out since in this case there won't be any SSV related security pop-up.

Steps to reproduce:
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1) Install 1.5.0_10 along with 6u10
2) Run following applet(requesting 1.5.0_10)
http://nicole1.sfbay.sun.com:8080/plugin_tests/JNLPSupport/desktopInteg/MultiJRE/JRE1.5.0_10Test.html
3)Security pop-up should be there
CLick on the "Run", applet should get loaded fine using 1.5.0_10
Try to drag the applet out of the browser window, if operation fails then bug is reproduced.

WORKAROUND:
4) Reload the page, and this time Click "Cancel" on the security pop-up.
Applet should get loaded using 1.6.0_10
5) Try to drag applet out of the browser. This DnD will work