C# - Datalist RepeatDirection.Vertical Shows Horizontal - Set Repeatcolumns In Code Behind?

i have a datalist in my aspx like this:

<asp:DataList
ID="dlSubs"
runat="server"
CellPadding="0"
CellSpacing="5"
RepeatDirection="Vertical">...</asp:Datalist>

when i do this in the code-behind:

this.dlSubs.DataSource = dtCat; // dtCat is a datatable with about 13 rows
this.dlSubs.DataBind();

everything gets rendered in one column (vertical) but i want two colums... so i do this:

DataTable dtCat = shop.DAL.ArtikelenDB.GetLeftMenu(Convert.ToInt32(Request.QueryString.Get("catg")));
double tmpDouble = (double)dtCat.Rows.Count / 2.0;
double repRow = Math.Ceiling(tmpDouble);
dlSubs.RepeatColumns = Convert.ToInt32(repRow);
dlSubs.RepeatDirection = RepeatDirection.Vertical; // also tried without this line...
this.dlSubs.DataSource = dtCat;
this.dlSubs.DataBind();

but when i do the above. it gets rendered horizontally... how is that possible?