Custom drop down cell not working with latest Silverlight Studio release

I have a custom datagrid column/dropdown cell that I have been using for a long time. We just updated to the July release Silverlight Studio DLLs 5.0.20132.340 and it is no longer appearing or dropping down when BeginEdit() is called for the cell. I reverted the DLLs back to the prior version we had (a patch version, 5.0.20131.320) and the drop down works fine in that version. A change between the two has caused a burp in our code.

I have usually been very good about taking the time to put together small samples to demonstrate, but it would be difficult for me to do that at the moment. I’m hoping you can help me think of some ideas for fixing the issue as is.

Here are the main parts of the code, which have worked for over a year:

In the datgrid AutoGeneratingColumn code:

if (e.Column.Name.Contains("SpecialColumn"))
            {
                string colName = e.Column.Name;
                e.Column = new SpecialDropDownColumn(e.Property)
                {
                    Name = colName,
                    HorizontalAlignment = HorizontalAlignment.Center,
                    Binding = { Converter = new SpecialKeyImageConverter() },
                    AccountDataProvider = this
                };
            }

In LoadedCellPresenter handler, I subscribe to mouse-up.
In the mouse-up handler, I check to see if it’s my special custom cell, then call BeginEdit() on the cell. In the prior version, this caused my custom cell to display its popup window.

if (cell.Column.Name == "SpecialColumn")
            {
                Dispatcher.BeginInvoke(() => _gridData.BeginEdit(cell));
                return;
            }

I could send the custom code for the column and cell if that would help, but it would be hard for me to break it out separately into a running sample. I’m hoping you have some idea why BeginEdit might not be invoking my custom cell. What happens when BeginEdit() is called for a cell? I have put breakpoints everywhere in my custom column, cell, etc class and nothing happens when BeginEdit is called.

Thanks for any ideas you can pass along. Sorry for not having a sample, I have a good record of doing that, usually.

Don