On Windows, the first column ignores this member and is always left aligned. You can work around this by inserting a dummy first column with width = 0 then putting your actual data in the second column, which does respect the alignment.
This is a quirk of the operating system's implementation going back a very long time and is unlikely to ever be fixed.
Alignment of the text in the cell. Applies to the header as well as all data in this column.