About closed object

In Rhino, if an object is not watertight, why does it become closed after exploding and then recombining it? I’ve been thinking about this for days and have asked many people, but no one has been able to explain it to me. Could anyone please offer some guidance? Thank you so much
test1111.3dm (1.5 MB)

Have you checked to see where it isn’t watertight? That is where I would start.—-Mark

help me

It’s not some grand mystery, it was just some quirk of how it was built in the first place that certain edges were left unjoined. It’s not some general fact that this will happen.

Probably a problem of tolerances when importing geometry…

Thank you! I’ll look into it further based on the hints you’ve provided

If it’s an issue of tolerance, why does the object become closed after exploding it, selecting all, and then recombining? This process doesn’t involve adjusting the tolerance at all."

Was this built in Rhino or imported? And if imported, how?

I opened it in Rhino 7 without any errors, but it shows as an open object. When I opened it in Rhino 8, it reported an error, but it displays as a closed object

Hi -

I’m not seeing any difference in behavior between Rhino 7 and Rhino 8.

As Jim said, this is not something that normally happens, and the reason for it happening with this file is impossible to find out at this point. As Jim asked, was this object created in Rhino from scratch or imported from some other source? Only if you can provide step-by-step commands to create an object that behaves in this manner, will we be able to pinpoint - and perhaps fix - what is happening.
-wim