Frozen properties don't seem to work in RT/XAML

I have a C1FlexGrid in Xaml, using C# as code-behind.

It is dynamically generated, meaning that the columns are read from the rows I send it. Generally all working OK. I can format columns hidden, give background colors, formatting, all that works fine.

I’m trying to freeze the first column, but I can’t make it stick. I’m doing this line of code in a routine called from OnPageLoaded (and subsequently called every time the grid is loaded with a new data set):

forecastGrid.Columns.Frozen = 2;

In the debugger I can see the property takes the value I give it, but the columns are never frozen, they scroll off the left as if I had made no attempt.

Have I done something out of sequence? The property seems very straightforward in the docs.

Also, I found in the docs the following two properties which might be helpful, but these properties don’t seem to exist:

http://helpcentral.componentone.com/nethelp/FlexGridWinRT/#!XMLDocuments/FlexGridRef/html/P_C1_Xaml_FlexGrid_C1FlexGrid_FrozenRows.htm

http://helpcentral.componentone.com/nethelp/FlexGridWinRT/#!XMLDocuments/FlexGridRef/html/P_C1_Xaml_FlexGrid_C1FlexGrid_FrozenColumns.htm