Steps to reproduce:
1. Install JDK 6u21.
2. Once install is complete, delete jdk1.6.0_21.
3. Uninstall JDK 6u21 from Control Panel. Uninstalling progress window comes up but then goes away and 6u21 is not removed from the list of installed programs.

When I tried to reinstall the same JDK, it gave a pop-up asking if I want to reinstall it as I already have it installed. Once I click on Yes, it tries to remove 6u21 but is unable to do so and then again the same window pops up.
Deleting of registry keys does not help.

I tried on Vista 32-bit with 6u21 b07.