When initially entering a variable name by clicking the empty name box and starting to type, after a short period the text box blanks out your input. If you click onto a different entry then your input appears again.
Also, when tabbing from name to the value field it actually takes you back to the top of the list instead of the next column.
Thanks for getting in touch! We are sorry to hear that you are having a hard time with the UI. We have a UserVoice for improving the UI which covers all the points you bring up and it already has quite a few votes.