This is problem in Eclipse SR1. You should switch back to R (SR0) release, next you can install PDT 3.3.1 from marketplace.
See also bug report on bugzilla
Problem is fixed in nightly builds: http://download.eclipse.org/tools/pdt/updates/3.4-nightly/
We released new stable (3.3.2) version with fix for this problem. You can find it on marketplace or in this update site: http://download.eclipse.org/tools/pdt/updates/3.3.2/