I just wanted to jump in here because I was having the same problem of the rc2 package not wanting to go away. It wasn't just leaving rc2 listed, installing and then uninstalling the more recent version wasn't deleting the plug-in either.
I believe I'm restating something that was already said (my brain didn't register what you said about the packages grid until after I'd gone through this), but I was always troubleshooting this at the end of the day, like today, and my brain is fried, and I needed small words. This is what I finally did:
1. Click Update to get and install the most recent version (rc4).
2. Click View Details to open the Package page, and click the Uploaded Versions tab.
3. Right-click version rc2 and click Remove Package Version. Then close to go back to Package Management.
4. Uninstall and remove rc4. It's really actually gone now.
Nothing personal, I'd just installed a lot of stuff on my site recently when I was testing for another project, and I'm trying to clean things up a bit and figure out what I'm actually using. It looks like something I probably will use at some point, I just didn't want the broken version sitting there staring at me.