It's not an error.
You could manually edit the items file on your machine and turn off the show weapon on back flag (afaik there is a tool for editing the items file), or get used to it. I use a glaive and the damned thing covers a good part of your reticule at certain angles, too, but I'd hate it if they took out it showing on the back for everyone, just looks good slung there when you're not trying to shoot things.