Ipad uses cellular data instead of wifi

Today I discovered that my iPad apparently has a software or hardware glitch which can cause it to ignore the perfectly good Wifi network it is connected to, and instead use the cellular data connection (and incurring significant costs in the process.)

I was at home (where I have a strong Wifi signal that my ipad is always connected to) and went to update all of my apps from the App Store. After I started the process, I started getting the warning messages informing me that some of the apps were larger than 50 MB and would have to be downloaded using wifi. Thinking this was strange, since I WAS using Wifi (and the little Wifi indicator was showing full signal strength), I went back and tapped "Update all" again, only to get the same messages. It was then that I received the warning that my AT&T data plan was almost exhausted. I immediately went and turned off Cellular Data, an inconvenient workaround that I'm unlikely to remember to do regularly, but that did force the iPad back to the Wifi that it should have been defaulting to.

I have no idea how long the iPad was using cellular data instead of wifi, but I suspect it was not just for a short period — my data plan should not have been anywhere near exhausted. And I wonder how many times it might have occurred in the past — there have been a few times that my data plan seemed to run out of data when I'd hardly used my ipad outside of wifi range.

This is clearly a serious bug, and one that can cost people a lot of money (Apple: you owe me $30 and perhaps more.). I did a search and found some mentions of this (or a very similar) bug being reported in the iPhone 5 last October, but I found no mention of a fix.

It's a bit appalling to think that Apple could let a serious problem like this exist for such a long time without a solution.