When riding a pig or minecart and using F5, the hand of your character is positioned so it looks like it's pointing to the left instead of the right. This does not affect gameplay, it's a just a graphical bug that's pretty annoying...
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Can't reproduce. Hand is still ... handy and on the right side.
For me, it only happens if I open my inventory or F5 while riding any sort of vehicle, or in SMP when other players near me are in minecarts.
@spartalaughs same happens for me. Kind of funny but it gets annoying.
Any screenshots?
I have added two screenshots, the first is before hitting F5/opening inventory and the second is after. It persists until I open my inventory or hit F5 while outside of the minecart or other vehicle.
I have this on several occasions, though never after riding. For me it happens randomly, more often after being affected by a Jump Boost-3 effect (custom plugin of server).
I've added another screenshot. I duplicated it by getting on the pig, pressing F5 twice, then getting off the pig and my hand looks like that.
i hope this gets fixed soon it really bugs me for some reason
If you look at yourself (F5) in a minecart, or if you look at the character within the inventory, you can see the hands are tucked into the minecart. The graphical bug is probably due because of this 'tucking in' feature.
Also in 1.6.2; I just tested it.
Happens with boats, too.
It's strange: The hand is normal when I get in the entity, then after I press F5 three times it looks like that. Then when I get off the entity, it's still to the right until I press F5 three times again. After that, it's back to normal.
I'm going to upload some screenshots.
This happens with anything you can mount!
Also added 2 snappys
this is the most annoying bug in the world
I see this happen occasionally. When it does happen it is a very noticeable bug. This can be distracting to many players.
Still happens in 1.7.4
Still happens in 14w05b ...
Very sad that it still not fixed since all that time.
You know what? This isn't about F5, it's about having a player riding something on your screen.
Try it in multiplayer.
I saw a video recorded in Beta that had this happen, so it's actually a very old bug.
The video is "Minecraft Ghost".
This is still a noticeable issue, and is not limited to F5 or the three entities mentioned in the title. It happens for all entities, no matter where they are on the map.
Confirmed for 14w19a.
Confirmed for 14w27b.
Edit: Also happens with boats.
Edit #2: This can be reversed by opening your inventory.
confirmed for 14w32b
Confirmed for 1.8pre2. Relates to MC-2963
Confirmed for 1.8.3.
Confirmed for 1.8.4.
Even when you dismount, the hand still points that way.

Reproduced on 1.8.7. To reproduce:
1. Make sure that there is nothing in your hand.
2. Get on a pig, horse, minecart, or boat (IE, anything that you can ride).
3. Observe that your hand is currently in the normal position.
4. Open and close 3rd person view (F5) or your inventory (if in creative, you will need to switch to the survival inventory tab).
5. Observe that the hand is now messed up.
6. To reset the hand position, exit the vehicle and then open and close 3rd person view or your inventory.
The hand's position changes whenever the player model is drawn (which happens in the inventory and in F5). And a player's normal 3D model does change when in a boat/minecart/ect – the hands are brought forward. But that shouldn't apply to the 1st person view one (or at least, it shouldn't remain in the changed state).
I made a mod in 1.7.10 to add rendering support for 1.8 skin format (by copying 1.8 code, sorry, I really want to use those skins).
In that process, I encountered this rendering issue, and I managed to fixed this issue.
If any of the mojang dev is interested in how I fixed this issue, here is the commit that fixed it: https://github.com/zlainsama/SkinPort/commit/d86b2d7670c0ab0fca98d474882583f286ec7a9f
What happened is the information used to render the player model isn't cleared after rendering, and it also does not get reset before rendering the first person hand.
Mod source repository: https://github.com/zlainsama/SkinPort
Fixed, no longer an issue as of 15w44b.
Can reproduce in 1.8.8, but not in the latest snapshot. Thus, no longer a concern.