When playing Minecraft and then putting your device into sleep mode and then unlocking it again, the game will freeze. Touch controls and physical buttons do nothing to affect it. When reselecting it from the app switcher, the game will appear to have moved and will reflect changes in the environment or any physical buttons pressed.

For example, say I pressed the menu button while playing the game. Nothing will happen unless I use the app switcher to return to the game, where the game's menu will have popped up.