If you have an Easy Chart in Realtime ChartMode and have Calculated (Constant Function) pens, the constant lines will not draw as the chart scroll/pans across the screen. They are only drawn on the initial load, or if you perform a zoom or a reset axis on the chart. SQL Tag Historian pens do update and draw. This is in version 7.2.6.
Thanks for bringing this to our attention - it has been fixed for 7.2.7.