Background apps show old info...security issue?

Question

So have you ever double clicked your home key to turn off apps or switch to another one running in the background?  The small screengrab shows the app, and most of the time its the last thing on your screen. Sometimes, for example, in my email app, the screen grab is of an email deleted and purged from weeks or months back. When the app is touched and opened, that old screen shot goes away and the last most relevant info is showed.
This concerns me. Sometimes, that old email, or message has confidential information and it is readable. It isn't even in my ipad anymore, but is showing like that.
Any info would be nice.

Answer 1

That setting is turned to on but that is not the issue. My issue is completely different.
For example, you get an email, read it, delete it, purge your trash file.  Three weeks later you double click home key to see what apps are running in the background and notice your email app or message app is open. There in that small screen grab is that deleted email, or message conversation that is no longer even on your ipad....complete and readable even though its a smaller image.
Then you tap that app to open it, the screen refreshes and that old deleted non existent email, message thread etc vanishes and the actual updated info shows as it should.
Where is the ipad storing that information to use as a display of background running apps?