I'm having issues with a split line in a sheet metal part. I've attached a sample part for reference.

I make a part using base flange and add a couple Miter Flanges, I then add a split line box to one of the faces. When I make a drawing and select the flat pattern the split line disappears. When I go back into the model in the flat pattern configuration the split line doesn't show.

Is there a way to have the split lines show when using flat pattern? I know I can use the unfold command and the split line stays but not when I use the flatten.

Here is the finished part:

Here is the flat pattern:

Here is the unfolded one: