Patch Set 1:

You need to have the ChangeId: footer in the commit message in order to tell Gerrit that new patchsets should replace older ones for the same change [1]. Either put that manually into the second patchset or install the Gerrit commit-msg hook [2] (this only works if you commit using native git since EGit doesn't support hooks yet).

[1] http://gerrit.googlecode.com/svn/documentation/2.1.2/user-changeid.html
[2] http://wiki.eclipse.org/EGit/Contributor_Guide#Install_the_commit-msg_hook_in_your_repository