If it updates fine in Max viewport but not in IR, then it's probably just another bug ;)
This leads to the very basic question: what exactly should be rendered by IR?
That what you see in the viewport? Or: That what would be rendered when you hit "render"?
The three key situations for me are:
1. When you have a Xref scene (for me still the one and only way to assemble large scenes) and it is not set to "Visible" in the Xref Scenes dialogue so that you don´t see it in the viewport. Should it be rendered in IR? At the moment it does render that Xref scene.
2. When you ALT-Q something (isolate it): Should the other non isolated objects be rendered by IR? At the moment it does not (but still any xref scenes!)
3. When you do a "Hide by category". Should the hidden objects be rendered by IR (and by standard render, but that´s another topic which hopefully will be discussed some day)? At the moment it does.
Isn´t IR meant for quick tweaking/previewing? For me personally it should always only render what´s in the viewport. So the behaviour for every of the three situations is not what I would like to have for a quick preview tool (IR).