Compositor vs GIMP/Photoshop (conver premul mismatch)

I exported some PNGs of 2 render layers with alpha, and stacked them in GIMP as individual layers (background and foreground). However, the final result from the same render layers in the compositor only matches if I used the “convert premul” option in the overlay nodes (and as I understand it this is incorrect for combining layers rendered this way).

Is there a way to avoid pre-multiplying the alpha of the PNGs on export (I thought that was PNG standard)? Or is there a way to take into account the pre-multipltied alpha in PNGs exported from Blender?



Anyone have any ideas?