This method is used to fix some layout issues of the editor. For each call of this method, the editors content grows with one BR element. Due to that the content area is getting with additional lines.

A possible resolution is incorporating the following override that fixes the onParentNodeChanged method: 

<telerik:RadEditor runat="server" ID="RadEditor1">
</telerik:RadEditor>

<script type="text/javascript">
	var oldOnParentNodeChanged = Telerik.Web.UI.RadEditor.prototype.onParentNodeChanged;

	Telerik.Web.UI.RadEditor.prototype.onParentNodeChanged = function () {
		oldOnParentNodeChanged.call(this);

		if (this.get_filtersManager().getFilterByName("MozillaRemoveLastBr")) {
			this.get_filtersManager().getFilterByName("MozillaRemoveLastBr").getHtmlContent(this.get_contentArea());
		}

	};
</script>