Do you have any accessibility options turned on? Two iPhones doing the same thing almost has to be something you're doing. If you can't figure it out, attach your phone to iTunes, make a backup to your computer, and reset the phone. Don't restore your data right away but instead test it to see that it's not doing the same thing. If it's OK, restore your backup. After restoring the backup, if it does it again, then you'll know that's it's either a setting or some software you installed.