Hello Tom Jaspering,
Indeed the article is a bit misleading - we will shortly fix that. We added to your Telerik points for pointing this out.
Regarding the issue itself - if the Menu is in an iframe (frame), it will not be able to expand over (out of) the frame. So, the solution will be to move the Menu in an upper frame as shown in the KB article. In this case the Menu will be able to expand over the iframe.
I hope this makes things clearer.
the Telerik team
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