Are all buttons visible in standard view mode? Does the problem happen only in full screen mode?
Have you fired the EnsureToolsFileLoaded()
method before adding the custom buttons to the RadEditor1.Tools collection?
If the problem happens in full screen mode, make sure that the ContentAreaMode property is set to Iframe, because currently there is a problem with the full screen mode in the Div mode.
All the best,
the Telerik team
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