I'm using the latest internal build (2010.2 0903) - also tried 2010.2 0812, the following causes issues with the axis:
<telerik:RadChart Name="DailyChart" Height="274" VerticalAlignment="Top" BorderThickness="0"
Background="#00000000" AxisForeground="White" Margin="0, 0, 0, 10" Visibility="Collapsed">
<telerik:RadChart.DefaultSeriesDefinition>
<telerik:SplineSeriesDefinition ShowItemLabels="False" ShowItemToolTips="True" />
</telerik:RadChart.DefaultSeriesDefinition>
<telerik:RadChart.DefaultView>
<telerik:ChartDefaultView>
<telerik:ChartDefaultView.ChartArea>
<telerik:ChartArea>
<telerik:ChartArea.AxisY>
<telerik:AxisY AutoRange="False" MinValue="0" MaxValue="1" Step="0.2" />
</telerik:ChartArea.AxisY>
</telerik:ChartArea>
</telerik:ChartDefaultView.ChartArea>
</telerik:ChartDefaultView>
</telerik:RadChart.DefaultView>
<telerik:RadChart.PaletteBrushes>
<SolidColorBrush Color="RoyalBlue" />
</telerik:RadChart.PaletteBrushes>
</telerik:RadChart>
Note the auto range and step in the axis. Looks fine in design mode, but when rendering the real chart it doesn't show the top value (1). If I change the step to just about anything else (0.25, 0.1, anything) it works fine, so it looks like a bug.