Render elements with backburner issue

[brad_]

So I'm rendering a large image (6000x9000) and I'm using split scan lines with backburner to do it. The image itself finishes and stitches together fine, but the elements are wrong.

It doesn't rename each element slice as it goes, instead it just overwrites the previous one. I'm using vray but I tried a test with scanline and it does the same thing.

 

So I end up with all the overall image strips ex. _STP0000_cam1, _STP0001_cam1 and so on.

 

The render elements will only have for example cam1_Alpha0000 and it will display the alpha for the last strip, not the first one, as backburner was just overwriting the file with each new strip.

 

Any idea how to fix this?