Edit and Fusion give different blur results

Why is there a difference between the Edit tab and the Fusion tab with blurs and alpha handling.
Both identical default Gaussian Blur values.
Obviously Fusion is doing what I expect but am I missing something re pre multiplying etc in the edit tab?

Gaussian Blur Edit.jpg (75.06 KiB) Viewed 682 times

Gaussian Blur Fusion.jpg (77.78 KiB) Viewed 682 times

Fusion works in Linear gamma. Maybe that?

Not sure colour space or colour management has anything to do with it, though you do get better/cleaner results working in linear.... I did not set up any linear conversion nodes for this simple test