Fix bug in continuous apply, test=develop (#27337)

python/paddle/fluid/optimizer.py

@@ -3570,8 +3570,10 @@ class ExponentialMovingAverage(object):
                 # bias correction
                 with layers.control_flow.Switch() as switch:
                     with switch.case(global_step > 0):
-                        layers.assign(output=ema, input=ema / (1.0 - decay_pow))
+                        layers.assign(
-                layers.assign(input=ema, output=param)
+                            output=param, input=ema / (1.0 - decay_pow))
+                    with switch.default():
+                        layers.assign(output=param, input=ema)
 
         self.restore_program = Program()
         block = self.restore_program.global_block()