Automatic Downloads not working for apps

I have Automatic Downloads turned on for apps on my iPhone And iPad. When I buy or "get" a universal app on my iPhone then it automatically downloads correctly on my iPad. When I downlnoad on my iPad though I get the app icon greyed out and showing as "Waiting...". It's been like this for months now. At firwt I thought it was because my phone was on 3G and it would download automatically when I get wifi, but it doesn't. The only time me it appears is when I sync with iTunes.

DOes anyone know know any fix?

thanks