- Moved most of the stuff happening in startGame outside of the swingWorker (to fix the ConcurrentModificationException error).

src/main/java/forge/gui/home/quest/SSubmenuQuestUtil.java

@@ -294,6 +294,15 @@ public class SSubmenuQuestUtil {
                 qData.setCurrentEvent(event);
                 qData.save();
 
+                return null;
+            }
+
+            @Override
+            public void done() {
+                SOverlayUtils.hideOverlay();
+            }
+        };
+        worker.execute();
         PlayerStartConditions humanStart = new PlayerStartConditions(SSubmenuQuestUtil.getCurrentDeck());
         PlayerStartConditions aiStart = new PlayerStartConditions(event.getEventDeck()); 
 
@@ -327,15 +336,6 @@ public class SSubmenuQuestUtil {
 
         Singletons.getModel().getMatch().initMatch(GameType.Quest, msh.getPlayerMap());
         Singletons.getModel().getMatch().startRound();
-                return null;
-            }
-
-            @Override
-            public void done() {
-                SOverlayUtils.hideOverlay();
-            }
-        };
-        worker.execute();
     }
 
     /** Duplicate in DeckEditorQuestMenu and