No - that's just right, you've not done anything wrong.
OK - we have to teach the iPad who's boss!!!!
To begin with we'll be a bit gentle then, if the iPad doesn't take the hint, we'll roll out the big guns!!
Let's shut the iPad down (unless you've already tried this) rather than just putting 'her' to sleep. Press and hold the Power button until the slider control comes up. Slide the slider control in order to accept the offer to power down. A rotating white bezel will appear in the screen as the iPad powers down.
When the screen had gone completely blank, press and hold the Power button again until the white Apple logo appears. The iPad will power up - it takes about 30 seconds. During this time the screen orientation is locked, so don't worry. Just before the power up is complete, the iPad plays a little jingle (tune) and, a few seconds later, you're up and running.
In fact Apple, on their website, recommend you power the iPad down on a regular basis anyway - it's good procedure and 'cleans things up'.
See if the problem persists. If it does - we'll 'up the anti' a bit.....
Don't worry, we'll sort it out...
Tim