Cylces Open exr multilayer export issues - 2.63

I struggling with multilayer open exr exports from cycles 2.63. In short, firstly, each time I render a scene, the animation frames chosen are never the same. If I start at frame 100 in the interface, the render files may start at any files around this number. Secondly, I am using the render node to a certain folder. The layers are often not consistent, sometimes getting all the layers requested, other times not. I also render at the same time using the render panel to a different folder. The layers are the same etc but the open exr content is not the same at all. Lastly, sometimes the app refuses to render past the frame so I have to start again. Also, the file sizes between the 2 render methods is huge. One gives me 12meg files, the other 128meg files. I use nuke to open the files. Anyone got any ideas where I am going wrong? Many thanks