Iain,
Interestingly I am not seeing this for any scenario where Dispaly Size >= Acquisition Buffer ... I tried values from 2 to 5000. It could be data sensitive. If you don't mind, can you export your data to a file (Tools->Save Memory) and send to us? If you prefer, you can email it to me directly (iali@ti.com).
Regards,
Imtaz.