I’ve seen the same problem (though not too often).
You may want to try is changing your bleed settings. I’m in book publishing, and I set it up so the bleeds are top, bottom, and outside. I have zero for inside. I don’t know what the printer folks like, but it doesn’t matter. We use their PDF settings and it automatically adds the bleed for all (top, bottom, inside, and outside). That usually fixes it.
I think InDesign overrides the right-hand master page art box because of the left-hand side inside bleed (which has nothing on it).
But if that doesn’t work–I have resorted to making my master page spread “unorthodox.”
By that I mean, I will make a CL (chapter opener left page). The left-hand page of the master is the opener with the art, and the right is a regular text page.
Then I will do the same with CR (chapter opener right page). The right-hand page of the master is the opener with the art and the left is a regular text page.
Then I apply the master page spread to the actual page spread. That also works.
It seems that doing it the normal way (as you definitely are), that Indesign ignores the picture box on the right because it’s touching the text master page. And the left-hand page has an inside bleed.
I don’t think you are applying the master to both spreads as you say it only happens on on right-hand side pages, but double-check as David suggests.
As an aside—are you applying the right-hand side master page by dragging down a master page on top of the required page, or option + clicking?
InDesign can definitely do weird things at times.
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