The RadEditor implementation in Sitefinity is the same as the one we're releasing with our DevCraft suite, so the same configurations apply.
In other words, to achieve the desired functionality you can:
1. Adjust the ContentFilters - for this particular scenario I believe you might need the ConvertInlineStylesToAttributes filter enabled. By default this filter is not enabled, as we use the Default filters collection, however you can specify explicitly which filters you'd like to use by going to Administration ->Settings->Advanced->Appearance->RadEditor filters for Content block widget (the property is of type EditorFilters, which will accept a comma delimited list of the desired filters, e.g. MakeUrlsAbsolute, FixEnclosingP, ConvertInlineStylesToAttributes )
2. Can you please provide us with some additional information on that case,s o we can make sure we're giving you an accurate advice?
3. You can control this behavior from Administration ->Settings->Advanced->Appearance ->
Please do not heistate to let us knwo if there's anything else we can help you with.
the Telerik team
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