From our support ticket communication, I learned that you use the Floating toolbar mode of RadEditor, but not the default one. I talked with one of our lead developers and he explained that that the ToolProviderID
Floating scenario in Multipage is unsupported. The ToolProviderID just copies the HTML of the Toolbar from the page and clones it across the editors on the page. When one of the editors, however, is hidden and the floating toolbar is still not created, the code could not copy non existing HTML content and apply it to the hidden editor.
That is why my suggestion is to either use the Default toolbar mode in your scenario, or just not set the ToolProviderID property.
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