Your expression should all result in the same exact data. I suggest a more detailed description of your chart set up. For example, is this text in a calculation field or did you use the "calculation" option for specifying this data for the x-series data to serve as chart labels?
Ok, I played around with it, I needed the Data Type in the Axis-options as text.
I got confused because I put "Show data points on chart"
Another expression that produces the same value that I prefer to use in such cases:
List ( "FirstText" ; "SecondText" ; "ThirdText" )