Shouldn't Blender free the GPU memory before rendering the next frame? I'm trying to render an animation, I can provide the .blend if necessary.

The problem is that if I render each frame as if it was a single render, it works fine. However, if I render it as an animation (multiple frames) I get OutOfMemory error when it reaches a certain frame (which I can render fine if I render just that single frame).  

I'm monitoring the GPU memory usage and it seems that the memory used in one frame is not being freed after the render is done. Is this the default behavior? If yes, is there a reason for it? If not, what could be causing it?

I'm using Blender 2.77 on Windows 10. My GPU is Nvidia's 980TI. 

EDIT

I found the actual problem. It was an add-on that supposedely shouldn't do anything related to rendering. It's called Perfect Shape. I disabled it and all renders worked fine, motion blur or not.
Might be a bug or a memory leak.

Blender does free unneeded memory as efficiently as it can, whoever it probably doesn't flush all memory when rendering an animation, as that would be highly inefficient.

There are immutable things that don't change between frames like geometry, materials, texture data, etc. and re-sending that unchanged data to the GPU every single frame would be a very big waste of time and resources and be very inefficient.

As such Blender tries it's best to be smart about it and keep as much relevant information in memory as it can. That being said memory management is probably a very hard task to do efficiently, and many times unneeded things are erroneously left behind. It's what I believe is called a memory leak (I'm not a programmer, I am hoping someone more enlightened in the matter than me will clarify or correct me here)

Over the course of rendering several frames those things build up and cause memory to reach it's limit.

That can probably be considered a bug and might be worth reporting to the tracker, I think. Although the chances of solving it are probably slim.

let's see what other have to say about it