After downgrading to Collaborator v6, I can at least select a whole changelist in the Perforce perspective, but the problem itself persists.
Here is some additional info:
The issue seems to be with the Perforce integration, not Eclipse itself. When I gave up with the Eclipse plugin, I installed the GUI application. When I tried to add the SCM configuration, autodetection didn't work. This may not actually be available for Perforce, but after clicking the Validate button, the client identified one of our Perforce servers. I have no idea where it found the information, but it was our main server, whereas I wanted to use our local mirror. Anyway, whether or not I filled in the fields by hand, the result configuration was the same, containing the main Perforce server. After proceeding, I tried to add a pending changelist to a review. Then, the client complained that there are no pending changelists. Even when I filled the P4PASSWD field with the wrong password, the client behaved exactly the same!
I would be happy if someone could get in touch with me since I'm not the only one with this problem in our company, and I'm willing to help with tracking down the problem.