For the time being you can use the following CSS workaround:
CSS:
	<style>
		.RadButton span.rbText {
			display: inline;
		}
	</style>
ASPX:
		<telerik:RadButton ID="rbACH" runat="server" ToggleType="Radio" ButtonType="StandardButton" GroupName="test" AutoPostBack="false" Text="eCheck" Width="200px" RenderMode="Lightweight">
			<ToggleStates>
				<telerik:RadButtonToggleState Text="eCheck" PrimaryIconCssClass="rbToggleRadioChecked" />
				<telerik:RadButtonToggleState Text="eCheck" PrimaryIconCssClass="rbToggleRadio" />
			</ToggleStates>
		</telerik:RadButton>