The zero-width space symbol is used in the Editor in order to work around browser issues in the Chrome browser concerning the selection of empty nodes. That is the reason why the ZWSP is used when using the font size with an empty selection.
There is a way to work around this issue. You can create a custom filter to remove the ZWSP. Here is a demo that shows how to use custom filters - http://demos.telerik.com/aspnet-ajax/editor/examples/contentfilters/defaultcs.aspx
. Your filter will traverse all the nodes in the content area and will replace all occurrences of the zero-width space char.
Hope this helps.
the Telerik team
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