Wireless flash exposure issues??

Hey fellow alpha users, something to try with wireless flash..

When in wireless flash mode, the pop-up flash acts as the wireless controller. It works just dandy most of the time, except when I get in close. If I'm within oh 5 feet or so of my subject, the pop-up flash affects the flash exposure. If I increase the shutter speed so it's in HSS the problem goes away. Another trick is I hold an index card in front of the pop-up flash.

Anyways, this came up during a conversation demonsmasher and I had last night, and I was just wondering if anyone else noticed this..

Try useing wax paper too. I heard that works good on popup flashes. Anyone know if this could damage a flash?