Setting persistence in XY mode results in the waveform disappearing completely. Do you have a plan to fix this bug? If you don't plan to support this the persistence option should at least be removed when XY is selected.
This is a basic oscilloscope feature and standard terminology. You call it persist and it's in the Display menu. It doesn't work in XY mode. I don't get a trace. Normally a picture is worth a thousand words but in this case "no trace" pretty much has it covered.