The step you have provided do not produce a closed shape.
If I presume that you checked the Cap (Flat) option when Offseting the Arc, I get results that fill in Illustrator like this, regardless of whether or not I use 5.3.2 (stable) or 5E63w (WIP)…
It doesn’t matter if the shape was closed or not. Trimmed circle is interpreted as single (closed)curve in stable version compared to multiple segments in WIP.
Sure. I am getting consistent results between Rhinoceros 5.3.2 (5D197) and RhinoWIP 5E75w using Epson drivers.
At this point, I’m lost; I don’t see what you see…and I don’t actually know what you expect to see. I am able to create closed curves from Rhino, Save to PDF, and fill them in Illustrator without issues…in both 5.3.2 and the current RhinoWIP (5E75w).
Perhaps you can post a simplified 3dm, please? If you can also post detailed steps for how you created this model, that would also be appreciated.
On my machine, a closed curve created in RhinoWIP (5E75w) that saved is to a vector PDF and opened in Adobe Illustrator CC opens as a closed (compound) path that is easily edited and filled.
I look forward to hearing what you experience in RhinoWIP 5E75w.