Adding a mid-weight master with alternate shape breaks interpolation

I have two masters Light (wght:0) and Heavy (wght:800) and between these masters, there are some alternating shapes (weight between 0-400). I want to add a mid-weight master (wght:400) from an instance but the interpolation breaks. Is there any way to make it happen while keeping layers compatible?
test.glyphs (4.1 KB)

The bracket layer is applied rather than just interpolated separately. Thanks for making us aware of this issue, I filed a bug report.