DPO7014 can’t determine saving CSV data range by programming command

When the scope recall length is 50K, I want to save scope channel 4 full data as csv file.

Trying the command as below:

data:stop 50000;

SAVe:WAVEform:FILEFormat SPREADSHEETCsv;

SAVe:WAVEform CH4, ,"C:\CH4";

But I always got 20K data length , not 50K that I set.

I have looked for the programming manual P.439.

In the manual, it could be use “DATa: STARt and DATa: STOP” command to determine what range I want to save.

But in real, it not so.