Hi Martin Roussel,
In its core, the RadHtmlPlaceholder is an IFrame that is rendered on top of the Silverlight plugin. Therefore, the rendering of RadHtmlPlaceholder's content is based on the browser's rendering mechanism for IFrames. Since we don't have access to this mechanism, we cannot do much about how the browser renders RadHtmlPlaceholder. However, you can set the RadHtmlPlaceHolder Width
properties. This way the control's size will be static and limited thus not allowing the described behavior.
As for the Unloaded event - there is no such event in Silverlight 3. You will have to create a custom one. However, I am not sure what logic you need to implement in this event. Perhaps if you can send us a sample project illustrating your scenario, we will provide you with a possible workaround.
All the best,
the Telerik team
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