Possible Bug ? Can't Boolean/Split Valid Closed Polysurface

Rhino
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1

Could be user error.. in which case I am not sure what I have done wrong !?
This is a valid polysurface as the result of a rail revolve of a single profile around a perfect circle.
I can’t seem to BooleanDifference / BooleanSplit / Split

You’ll see I have crated a ‘tool’ to try and do this (after failed attempts with Gumball slice / Single surface) none of which work..

nosplit.3dm (438.6 KB)

2

FYI I worked around by exploding and splitting and then re-joining.. still interested to know what makes the polysurface un-splittable