custom avatar dimensions set to 160x320, i upload 160x320 vbull shrinks it to 159x318

[sross]

Not sure why it is doing this, can anyone please advise? avatar page says upload max 160x320 so i upload 160x320 but vbull is resizing it to 159x318 not sure what is causing it to do this? Thanks for any help! also if i view just the image it is showing 159x318 so it has actually resized it..

It is also not a size issue i have allowed up to 300kb and it's only 72kb thanks