Hello Nicoleta,
Ok I see. This is unfortunately normal behavior. While the auto-detect option can in some cases detect datetime columns, other types of columns are always recognized as strings, and it is up to you to modify each column manually so that it matches the correct data type and it is processed as you need when the workflow is executed. Basically, what this option does is only detecting the columns of the sample file and general file formating such as separating character, etc.
If you need to modify the sample file, you will have to go reconfigure all the format options of all columns.
Florent.