Currently bugzilla-tool seems to error out if someone commits while land-patches is running because the final update step doesn't understand how to resolve-ChangeLogs.
Actually, bugzilla-tool could also use the update-webkit script (which runs resolve-ChangeLogs for you when it updates). However, update-webkit is currently broken-ish for svn-1.6: Bug 27168.
This is similar/same as bug 26865.
I think I"m gonna mark this as a dupe of bug 28316. The current suggestion is that when commit/update fails due to ChangeLogs we should just try the patch again from the beginning. Obviously you should reopen this if you don't believe it's a dupe. *** This bug has been marked as a duplicate of bug 28316 ***