Using Cellular Data When Connected to Wi-Fi (AT&T)?

I have an iPad 2 with internet access on AT&T. My billing cycle starts on the 10th of every month. On Monday of this week (7 days into this month's billing cycle) I received an email stating that only 20% of my data plan for the month remained. I have the 250MB/month plan, which historically has been sufficient for my usage (email, web surfing, normal stuff, etc.). Between the time when I received this message and today, I did not use my iPad. So, today when I opened up my iPad there was a message on the screen stating that I had less than 10% of my data plan remaining. I checked the status of my account and saw that I only had 7MB remaining. So, between Monday and today (Tuesday), I did not use my iPad, it was connected to a wi-fi signal the entire time, and I somehow used 43MB of data. The only apps that were running in the background when I turned my iPad on tonight were Mail and Safari. I do have my work email linked to Mail and set to automatically sync. I called AT&T tonight and they told me that even when I am connected to wi-fi I am using cellular data. I said that I didn't think that made any sense. Does it make sense? They said that the only way I can use wi-fi exclusively and not have it also reduce my monthly cellular data allowance is to turn cellular data off. I thought the only time that I was using cellular data was when I was not connected to wi-fi. Any insight would be appreciated. Thanks in advance!

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I am not sure if it makes a difference, but I have updated to iOS5. In prior months, my total data usage was around 190-200MB. I have somehow used 243MB in the first 8 billing days of this cycle and my usage has not really changed. Could this somehow be an iOS5 issue?

 

Anyone?

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Well, I found this thread in the Apple support forums:

https://discussions.apple.com/message/16169906#16169906

I have to admit that when my iPad 2 is not being used, it is not always plugged into power. So, maybe when my device is going to sleep and automatically syncing my work email it is pulling over 3G because the wi-fi antenna has been turned off to conserve power. As I have previously stated, I have my work email automatically synced to my device. I am guessing that this is where most of the mysterious data usage is coming from, especially since it is the only thing running in the background and I am using data even when I am not using the iPad. I am going to try to leave cellular data turned on and set my email to sync manually. I really only use my iPad 2 to check email on the weekends and when I am traveling. So, I have no real need for it to be syncing automatically. I will test this out and see what kind of results I get. In the meantime, if anyone has any additional insight, please advise.