Well, PyDev is comprised of a whole bunch of plugins, but they’re all named org.python.pydev.x_version. Same sorta deal with AJDT, with all plugins named org.eclipse.ajdt.x_version.
This is on MacOS X 10.4.2. I noticed I did not have this problem on my Windows XP computer. FWIW, I went from 4.0M2 to 4.0M3 on the Mac but started with 4.0M3 on the PC.