Problem when changing column type with Google Analytics

Hi,

Is have some thing like :

#"Added Items" = Cube.Transform(#"12345678", { [... some custom dimensions ...], {Cube.AddAndExpandDimensionColumn, "ga:date", {"ga:date"}, {"Date"}}, {Cube.AddAndExpandDimensionColumn, "ga:source", {"ga:source"}, {"Source"}}, {Cube.AddMeasureColumn, "Avg. Time on Page", "ga:avgTimeOnPage"}, {Cube.AddMeasureColumn, "Pageviews", "gaImage may be NSFW.
 Clik here to view.ageviews"}, {Cube.AddMeasureColumn, "Time on Page", "ga:timeOnPage"}}),
#"Changed Type" = Table.TransformColumnTypes( #"Added Items",{{"[... a column name ...]", type date}})
in
#"Changed Type" 

The column was a text column, and I change it to Date, all the other column are change to Text, so I lose every single type except the new one.

Like "Time on Page" or "Pageviews" are now Text Column.

Any idea why?

*Edit : Same thing happen when I add a new column, all the columns are transform to Text.