I am curious if the command being sent to Tabcmd is for the same view - per - Exporting a CSV of Underlying Data Using Tabcmd Export or Get | Tableau Software ?
Also - another option to compare is just to add .csv (replacing the "?" on the url) to the url of the browser when viewing to create a csv file.
Have you found the reason? I have the exact same problem. The csv is exported from Tableau desktop is alright, just like your Pic1. However, the csv is exported by using tabcmd is wired, just like your pic 2.
I actually do not remember in what panel had this issue but what i do is to generate a special tab in table layout for the info i need to email in CSV and that's it.