Player's and Horses head while riding having strange behaviour when looking at the skin in the inventory

This bug still occurs in 13w24b. It happens in any situation when you open, in the 3rd person view both front and back views, any inventory that have a thumbnail with player's model. You don't need to be ridding a horse, this just makes the bug more noticeable since the inventory window covers a big portion of the screen.

In 1.5.2 and 13w24b, the player's head rotates 45-90º towards the mouse pointer and it's likely to shake rapidly depending on the distance between the camera and the player. Upon closing the inventory window, you'll see the head rotating back to its normal position. If you install ShoulderSurfing mod, you can move the camera sideways a bit so you'll be able to see clearly the issue.

It's not something that could harm the gameplay, but it's an issue for those who record videos: it seems the player is having seizure.

My guess is that, there's a conflict between the "preview" model in the inventory and the in-world player's model. Either they should disable any movement of the in-world player's model whist the inventory is open or make both in-world and inventory player's model synchronize with each other. The latter is a more elegant solution, in my opinion.

Added a screenshot taken with ShoulderSurfing mod which was used to displace the camera/view sideways so that it's easier to see the bug occurring.

Very easy to fix. Mojang forgot restore after rendering the rotationYawHead field in entity class.
From (Class "GuiInventory" by MCP mapping):

===== START ======
    public static void func_110423_a(int par0, int par1, int par2, float par3, float par4, EntityLivingBase par5EntityLivingBase)
    {
        GL11.glEnable(GL11.GL_COLOR_MATERIAL);
        GL11.glPushMatrix();
        GL11.glTranslatef((float)par0, (float)par1, 50.0F);
        GL11.glScalef((float)(-par2), (float)par2, (float)par2);
        GL11.glRotatef(180.0F, 0.0F, 0.0F, 1.0F);
        float var6 = par5EntityLivingBase.renderYawOffset;
        float var7 = par5EntityLivingBase.rotationYaw;
        float var8 = par5EntityLivingBase.rotationPitch;
        GL11.glRotatef(135.0F, 0.0F, 1.0F, 0.0F);
        RenderHelper.enableStandardItemLighting();
        GL11.glRotatef(-135.0F, 0.0F, 1.0F, 0.0F);
        GL11.glRotatef(-((float)Math.atan((double)(par4 / 40.0F))) * 20.0F, 1.0F, 0.0F, 0.0F);
        par5EntityLivingBase.renderYawOffset = (float)Math.atan((double)(par3 / 40.0F)) * 20.0F;
        par5EntityLivingBase.rotationYaw = (float)Math.atan((double)(par3 / 40.0F)) * 40.0F;
        par5EntityLivingBase.rotationPitch = -((float)Math.atan((double)(par4 / 40.0F))) * 20.0F;
        par5EntityLivingBase.rotationYawHead = par5EntityLivingBase.rotationYaw;
        GL11.glTranslatef(0.0F, par5EntityLivingBase.yOffset, 0.0F);
        RenderManager.instance.playerViewY = 180.0F;
        RenderManager.instance.renderEntityWithPosYaw(par5EntityLivingBase, 0.0D, 0.0D, 0.0D, 0.0F, 1.0F);
        par5EntityLivingBase.renderYawOffset = var6;
        par5EntityLivingBase.rotationYaw = var7;
        par5EntityLivingBase.rotationPitch = var8;
        GL11.glPopMatrix();
        RenderHelper.disableStandardItemLighting();
        GL11.glDisable(GL12.GL_RESCALE_NORMAL);
        OpenGlHelper.setActiveTexture(OpenGlHelper.lightmapTexUnit);
        GL11.glDisable(GL11.GL_TEXTURE_2D);
        OpenGlHelper.setActiveTexture(OpenGlHelper.defaultTexUnit);
    }
====== END =======

To:

===== START ======
    public static void func_110423_a(int par0, int par1, int par2, float par3, float par4, EntityLivingBase par5EntityLivingBase)
    {
        GL11.glEnable(GL11.GL_COLOR_MATERIAL);
        GL11.glPushMatrix();
        GL11.glTranslatef((float)par0, (float)par1, 50.0F);
        GL11.glScalef((float)(-par2), (float)par2, (float)par2);
        GL11.glRotatef(180.0F, 0.0F, 0.0F, 1.0F);
        float var6 = par5EntityLivingBase.renderYawOffset;
        float var7 = par5EntityLivingBase.rotationYaw;
        float var8 = par5EntityLivingBase.rotationPitch;
        float savedHeadYaw = par5EntityLivingBase.rotationYawHead;// <----- ADDED THIS LOCAL VARIABLE FOR STORING CURRENT HEAD ROTATION
        GL11.glRotatef(135.0F, 0.0F, 1.0F, 0.0F);
        RenderHelper.enableStandardItemLighting();
        GL11.glRotatef(-135.0F, 0.0F, 1.0F, 0.0F);
        GL11.glRotatef(-((float)Math.atan((double)(par4 / 40.0F))) * 20.0F, 1.0F, 0.0F, 0.0F);
        par5EntityLivingBase.renderYawOffset = (float)Math.atan((double)(par3 / 40.0F)) * 20.0F;
        par5EntityLivingBase.rotationYaw = (float)Math.atan((double)(par3 / 40.0F)) * 40.0F;
        par5EntityLivingBase.rotationPitch = -((float)Math.atan((double)(par4 / 40.0F))) * 20.0F;
        par5EntityLivingBase.rotationYawHead = par5EntityLivingBase.rotationYaw;
        GL11.glTranslatef(0.0F, par5EntityLivingBase.yOffset, 0.0F);
        RenderManager.instance.playerViewY = 180.0F;
        RenderManager.instance.renderEntityWithPosYaw(par5EntityLivingBase, 0.0D, 0.0D, 0.0D, 0.0F, 1.0F);
        par5EntityLivingBase.renderYawOffset = var6;
        par5EntityLivingBase.rotationYaw = var7;
        par5EntityLivingBase.rotationPitch = var8;
        par5EntityLivingBase.rotationYawHead = savedHeadYaw;//<------ ADDED RESTORING HEAD ROTATION
        GL11.glPopMatrix();
        RenderHelper.disableStandardItemLighting();
        GL11.glDisable(GL12.GL_RESCALE_NORMAL);
        OpenGlHelper.setActiveTexture(OpenGlHelper.lightmapTexUnit);
        GL11.glDisable(GL11.GL_TEXTURE_2D);
        OpenGlHelper.setActiveTexture(OpenGlHelper.defaultTexUnit);
    }
====== END =======

That's all. Fixes both for player and horse.

Moderators, please put code in code tag _
Sorry for long comment

@Ksenofontov Alexander:
Tip: Put
{code}
... here is the code
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