I have the same problem with my iPad after upgrading to iOS 8. I am trying a full restore to see if that helps.
Note: No special keyboards involved as one commenter suggested. And trying to perform a 4- or 5-finger Multitasking Gesture more slowly as another user suggested does not work for me and is not a fix.
The only real way around it is to toggle the option off and back on in System Preferences (restarting and hard restarting are not required and do nothing to keep the issue from returning).
This is happening for all variants of iPads and iPad minis.
I have created Bug 18403607 with logs. If you have an Apple Developer account, go to http://bugreport.apple.com/ and file your own Bug and reference mine (or just reference mine), and attach your iPad's logs. Be sure to attach your logs (the form includes instructions).
The best way to make Apple aware of a bug like this is to file a Bug and get their attention based on volume of standalone Bugs or references to existing Bugs.