Explode and join loses top surface in rhino 5 but not 8

[davidcockey]

This post is a follow-on to Is this object watertight rhino yes and Anycubic Prusa and F360 no

@Steve1

Fixing non manifold edges I explode and join and the top surface vanishes in rhino5
do in 8 and all is good.

Explode and Join works for me in V8 with no loss of surfaces. Image below has original non-manifold object on left, fixed object on right.

Your object with the claimed lost top face has 3122 surfaces like all original object. It does have naked edges. When I exploded and joined the original non-manifold object there were no naked edges.