Hatching two objects creates line in between

[atuckerJKU9U]

Can anybody tell me what is causing the hatch on the left in the attached drawing to glitch and show a line between the two objects?  If cut a little piece out of the circle then close it so it becomes a polyline, it doesn't do it anymore.  I have plenty of workarounds, I'd just like to know why it is happening so I can avoid the situation.

[atuckerJKU9U]

It's something wrong with that top polyline.  Here's the same polyline interacting the same way with another one.  What is wrong with it?

[paullimapa]

After applying FLATTEN command:

[atuckerJKU9U]

Hmm, still doing it after using flatten for me.  What made you think that would help when neither of the objects are away from z=0 or 3d?  And why did it work for you and not me...

[paullimapa]

Typically when odd things happen with objects I would run the FLATTEN command.

I'm not sure why that didn't work for you though.

Did you open the dwg I posted to see if the Circle & Pline objects on the far right still works for you?

If so, perhaps copy & paste those into your dwg & see if that still works.

[atuckerJKU9U]

We do the same thing here.  I got a routine called superflatten just because so much stuff we get from engineers has z coordinates all over the place.  Anyway, the file you sent back does work for me as it did for you, but I noticed that something happened to the polyline so that the one you were hatching is not identical to the original.  Mine is the pink one, yours is the yellow one.  I think that's why they're acting different from each other, not from being flattened.

[paullimapa]

The Flatten command could have made adjustments to that PLINE object.

But I also noticed something else that's odd. 

When I open your dwg in AutoCAD 2020 the Hatch Preview still shows that line.

But once I complete the Hatch command the line disappears.

This odd self correcting behavior does not occur in 2021, 2022, 2023 or 2024.

But in all the other versions I would run the FLATTEN command actually on just the PLINE object and that resolved the issue.