diff --git a/earwigbot/wiki/copyvios/workers.py b/earwigbot/wiki/copyvios/workers.py
index ffe0b29..61ec917 100644
--- a/earwigbot/wiki/copyvios/workers.py
+++ b/earwigbot/wiki/copyvios/workers.py
@@ -96,29 +96,37 @@ class _CopyvioSource(object):
         self.confidence = 0.0
         self.chains = (EMPTY, EMPTY_INTERSECTION)
 
-        self._event = Event()
+        self._event1 = Event()
+        self._event2 = Event()
+        self._event2.set()
 
-    def active(self):
-        """Return whether or not this source needs to be filled out."""
-        return not self._event.is_set()
+    def touched(self):
+        """Return whether one of start_work() and cancel() have been called."""
+        return self._event1.is_set()
 
-    def complete(self, confidence, source_chain, delta_chain):
+    def start_work(self):
+        """Mark this source as being worked on right now."""
+        self._event2.clear()
+        self._event1.set()
+
+    def finish_work(self, confidence, source_chain, delta_chain):
         """Complete the confidence information inside this source."""
         self.confidence = confidence
         self.chains = (source_chain, delta_chain)
-        self._event.set()
+        self._event2.set()
 
     def cancel(self):
         """Deactivate this source without filling in the relevant data."""
-        self._event.set()
+        self._event1.set()
 
     def join(self, until):
         """Block until this violation result is filled out."""
-        if until:
-            timeout = until - time()
-            if timeout <= 0:
-                return
-            self._event.wait(timeout)
+        for event in [self._event1, self._event2]:
+            if until:
+                timeout = until - time()
+                if timeout <= 0:
+                    return
+                event.wait(timeout)
 
 
 class _CopyvioQueues(object):
@@ -231,12 +239,15 @@ class _CopyvioWorker(object):
             self._queue = None
             self._queues.lock.release()
             return self._dequeue()
-        self._queues.lock.release()
 
         self._logger.debug(u"Got source URL: {0}".format(source.url))
-        if not source.active():
-            self._logger.debug("Source is inactive")
+        if source.touched():
+            self._logger.debug("Source has been cancelled")
+            self._queues.lock.release()
             return self._dequeue()
+
+        source.start_work()
+        self._queues.lock.release()
         return source
 
     def _run(self):
@@ -371,6 +382,8 @@ class CopyvioWorkspace(object):
         self._logger.debug("Waiting on {0} sources".format(len(self.sources)))
         for source in self.sources:
             source.join(self._until)
+        with self._compare_lock:
+            pass  # Wait for any remaining comparisons to be finished
         if not _is_globalized:
             for i in xrange(self._num_workers):
                 self._queues.unassigned.put((StopIteration, None))
@@ -379,10 +392,10 @@ class CopyvioWorkspace(object):
         """Compare a source to the article, and update the best known one."""
         delta = MarkovChainIntersection(self._article, source_chain)
         conf = self._calculate_confidence(delta)
-        source.complete(conf, source_chain, delta)
         self._logger.debug(u"compare(): {0} -> {1}".format(source.url, conf))
 
         with self._compare_lock:
+            source.finish_work(conf, source_chain, delta)
             if conf > self.best.confidence:
                 self.best = source
                 if conf >= self._min_confidence: