Thanks, ahatisTW and MagmaMan. What you are observing is an issue that we will look to resolve. You may notice that the individual cell types in the newly generated column are DateTime type as expected, however the column type is incorrect. This should not impact your expected results in the data (the data in the new Col is DateTime as expected).
That's good to hear it's something that will be fixed/changed in a future release. Just to clarify, if you try to use the newly generated column in a Computed Column using any of the DATE formulas (DATEDIFF etc), the formula does not recognize the value as a date type. I believe it returns an error that it is a number.