When you begin to sprint or fly, the FOV of the screen changes, except the item in hand also changes with the screen. MCPC does not have this because it is not meant to be in the game. Therefore, its a bug. Device: All devices that can download Minecraft Pocket Edition
Please do not assume the differences between any editions of Minecraft are bugs. If you wish to request new features or tweaks for Minecraft: Pocket Edition, please use the Suggestions Forum or Subreddit.