Pop up Flash on A65
It's because it's recycling. If you're using full power the flash has to build the charge back up before it can flash at full power again. If you trigger the flash before it's had a chance to fully recharge it will go off with whatever charge it had built up (less than full power). However, if you are using a lower flash power setting you can probably do a few back to back before it needs to fully recharge.
Good luck and happy shooting!