iPad switches to cellular connection despite strong WiFi

iPad 3 with Wifi + Verizon LTE.

I have an excellent 802.11n Wifi network at home (Airport Extreme + Express). It works great with 12 devices, including Apple TV and this iPad. Signal strength and data throughput is top notch. Our internet connection is 50mbps Comcast cable.

Problem: While streaming video, the iPad switches silently from Wifi to Cellular data, consuming my cellular data plan.

I know that others have recommended turning cellular data OFF, which is exactly what I do when this happens. But that's not really a good solution, as the product is intended to handle this automatically.

Observations:

- This ONLY occurs while streaming video, usually through Hulu Plus. During regular use, the iPad remains properly connected to Wifi, no exceptions found.

- When this occurs, the status bar shows Verizion LTE and NO WIFI. Only by turning cellular data OFF do I get Wifi to return.

- Once cellular data is turned off, Wifi reconnects and video works normally.

I have reset Network Settings to see if this helps.

Any ideas, folks?

- Puzzled in Portland