Minecarts are shooting off of the corners of rails

Easy to replicate. Create tracks with curves, send a Furnace Minecart down the rail to push a Minecart with Chest, chest will derail.

I want to include that regular minecarts and probably altered ones to, speed up to an unbelievable rate when you have them run on small redstone rail hills repeatedly, and they fly straight off when they hit a corner and sometimes even glitch a few blocks outside of the corner at this speed.(the only problem with minecarts was they sink underground,why cant we get the same physics back from 1.7.5).

If it's a feature, it doesn't work in a logically or physically consistent way. I know the game's physics have never been realistic, but this is a turn for the worse.

You can have a cart travel northwards across many accelerator rails. If you make it turn northeast, then briefly north (as few as four blocks), and then northwest, it won't derail despite the near 90-degree turn. However, if you make it turn northeast, it will always derail if you try making it turn east, regardless of the distance it has gone diagonally, unless it has slowed down immensely.

This same issue applies for other directions: you can't get the cart to travel in excess of +/- 45 degrees of its original trajectory, however gradually you try to make it turn. Meanwhile, you can make it serpentine back and forth on tight curves without derailing, if it travels in the same net direction it was accelerated in.

The carts don't seem to have a notion of "wheel speed" or forward momentum; rather they have a separate momentum in X and Z. Although they have tolerance and won't derail when traveling within 45 degrees of their momentum vector, the vector does not change when the cart's direction changes. As a result, a north-accelerated cart will maintain zero momentum on the west/east, even if it spends extended periods of time traveling northwest or northeast.

I have a huge world which is connected mostly by rail. All rails exhibit this problem where the minecart derails on corners while traveling at high speed. We do not need that much realism in Minecraft. Had to go back to 14w10c for my rail system to work again.

This is a feature and Mojang is still trying to make it work more realisticly (properly).

I encountered a similar issue in my chicken vortex generator: Make a 4x4 rail square with three powered tracks on one side, drop a torch to power the track. If you place an empty cart (and push start it) it will barely make it around then hit the powered rail which will push it around again, this seems normal. Now put something (yourself, a chicken, etc...) in the cart and it begins to spin out of control, pretty quickly it will fly off the track.

I have a suggestion for Mojang on this - create a one-way braking track. When a cart would enter the track block from one direction, it would slow the cart by a specific factor. When entered from the other direction, there would be no effect. This would allow the core algorithm to be maintained, give us 'cart-buffs' another tool to factor into our designs, and still have the penalty for moving too fast on a curve.

I have two thoughts on this:
1> Make the amount of power applied to the cart proportional to the amount of redstone power applied to the track, so if only 1 RS power was applied it would only add a small amount of speed. The downside is this would make powering small track circuits unwieldy in the absence of resistors.
2> Add the inverse of the powered track (braking track) and remove the braking effect of non-powered powered tracks. For both powered and braking tracks, with no RS power applied it would behave as a normal track. Think of roller coaster brakes...

Fixed (probably in 14w17a)

Fixed or rolled back? If rolled back, can we expect the code to be re-introduced again in the future?