Is it possible that flattening "native elements" is different than "imported elements"?

[Roger Breton]

This is a follow-up to a post on the Illustrator group.

I created simple RGB objects that use Overlay blend mode in InDesign. Three separate RGB circles, colored with 255r, 255g and 255b. Their overlap shows up as 'cyan', 'magenta' and 'yellow' as expected.

The document Transparency Blending space is set to CMYK.

I have four distinct 'graphics' :

1) created in Photoshop "flattened"

2) created in InDesign "live" (unflattened)

3) created in Photoshop, in three separate shape layers

4) created in Illustrator, "flattened"

What I don't understand is why is the graphic created in RGB appears different from those created in Photoshop and Illustrator? Clearly, to the best of my understanding, it is as though, the native InDesign graphic is NOT being flattened in CMYK space but in RGB space, despite the setting of the Transparency Blending Space.

What am I missing?

[Roger Breton]

Here is a screen capture of the page, as it appears with Transparency Blending Space set to RGB *and* Proof Colors (Document CMYK) : all objects are flattened the exact same way :

Somehow, my intuition tells me that, setting the Transparency Blending space to RGB is preferable? Even if, on Export to PDF, everything is converted to CMYK.  It seems like a "workaround" to get a "consistent" output but at the expense of color saturation?