FYI: Works fine for me as "###,###.00" when the user is working in English but the formatting does not work for "###.###,00" when the user is working in French. When using the French numeric formatting, the Edit-mask control or the DataWindow edit-mask is not observing the mask and stays in English mode (as per the Windows control panel).
We have to support both formats here in Canada dynamically based on whether the application user has selected to work in either English or French - which they can also dynamically swap back & forth in as well. Looks like this is a bug in PB 12.6 to me.