The attachment should stay in the draft. Try quitting Mail and start over with a new email.
Go to the Home screen and double click the Home button. That will reveal the row of recently used apps at the bottom of the screen. Tap and hold on the app in question until it wiggles and displays a minus sign. Tap the minus sign to actually quit the app. Then tap anywhere on the screen above that bottom row to return the screen to normal. Then restart the app and see if it works normally.
I would start with the basics. Quit the iWorks apps - which ever ones that are doing this - and quit the mail app as well, restart the iPad, and then see if it will work properly.
Go to the home screen first by tapping the home button. Double tap the home button and the task bar will appear with all of your recent/open apps displayed at the bottom. Tap and hold down on any app icon until it begins to wiggle. Tap the minus sign in the upper left corner of the app that you want to close. Tap the home button. Restart the iPad.
Restart the iPad by holding down on the sleep button until the red slider appears and then slide to shut off. To power up hold the sleep button until the Apple logo appears and let go of the button.
I already tried your suggestion but the issue is not only on my iPad but in all the iPad I try to use.
If you try to create an email from a file generated by Neynote, numbers or pages and save that email as draft, once you resume that email from Mail and send it ,when the mail arrives to the destinatary no attachment is present ( it works correctly only with PDF ).Try by yourself and you'll see this is a bug.
My experiment shows the same results as what you are seeing. If I go to my email on the server, it will show the paper clip attachment indicating that there is an attachment, but when I open the email, there is no attachment in the message.
I am only using Pages and not using Keynote. It does work with PDF files as you stated, but not with Word or Pages files themselves. Very odd indeed.
Totally concur that this is a generic, repeatable bug - no matter what program initially created the draft.
It is an issue with the e-mail app dropping the attachment from the draft e-mail, upon send. as a draft e-mail, the attachment is present, but gets dropped on send (no attachment visible when you look at the e-mail in the Sent folder).
Just had the same issue trying to send a Word document, and it is repeatable every single time.
iOS 5.1.1, iPad v3.