Sheet metal opposing bends feature creation

Hi

I've created a sheet metal feature which has bends going in opposing directions from each other, see the attached image. The feature is essentially a rip across a bend with the corners of each bend folding at 90 degrees in opposite directions. When I try to flatten this part it gives an error.

I have tried creating this in two ways:

1. By adding a flange and then joining the open end using the join tool.
2. Making a form tool and punching the one shape into the other.

Both methods worked to create the feature but neither method works when I try to flatten the part.

What would be the best way to create this feature in order to create a flattened state?

Regards

David