diff --git a/dwtt b/dwtt
index da87024..a6512a6 100755
--- a/dwtt
+++ b/dwtt
@@ -46,9 +46,11 @@ def main(argv):
         if type(res).__name__ == 'bool':
             if not res:
                 break
-        else:
+        elif type(res).__name__ == 'str':
             # todo: move to GUI
             print "Error:", res
+        else:
+            print "Unknown return type '%s'" % type(res).__name__
 
 def doCmdWindow():
     c = CmdWindow()
@@ -66,12 +68,14 @@ def processStart(cmd, store):
     else:
         taskid = task.taskid
     store.updateCurrentTask(TaskRef(taskid, cmd.time))
+    return False
 
 def processOut(cmd, store):
     ct = store.getCurrentTask()
     if ct is not None:
         seconds = (cmd.time - ct.time).seconds
-        store.addTime(cmd.time.strftime('%Y-%m-%d'), ct.taskid, seconds)
+        if seconds > 0:
+            store.addTime(cmd.time.strftime('%Y-%m-%d'), ct.taskid, seconds)
         store.clearCurrentTask()
         return False
     return 'No current task defined'