[Plugin: WordPress Beta Tester] Still tries to download latest version of 3.3.x

WordPress 3.4 Release Candidate

To test WordPress 3.4, try the WordPress Beta Tester plugin (you’ll want “bleeding edge nightlies”).

Emphasis mine.

I have the same problem. When I try to switch to the bleeding edge nightlies, the radio button jumps back up to Point release nightlies when I save the settings.