uPnP visibility delayed on iPad

I have XBMC 12.2 installed on a Mac Mini HTPC, a MacBook Air, a Windows laptop, and an iPad 1, all on the same LAN.

XBMC on the MacBook Air and the Windows laptop see the HTPC pretty much instantaneously as a uPnP video source.

However, XBMC on the iPad 1 takes anywhere from five to ten minutes to see the HTPC.

Anyone have any idea why?