[v8i SS4 C#] Cannot open lots of files with print dialog open

We have a print addon for MicroStation that have worked on MicroStation v8i for many years. But now with ss4, if we try to select many files (10+), MicroStation crashes with the following error: Attempted to read or write protected memory. This is often an indication that other memory is corrupt. 

I have tried with new empty files to make sure that it's not corrupt files that causes the crash.

It's not easy to reproduce, but the code below will crash when I run in debug. The strange thing is that it only crashes if I have the print dialog open. If I comment out the first line, the code runs fine.

BIM.Session.Instance.Keyin("MDL LOAD PLOTDLG SILENT "); // works if this line is deleted
OpenFileDialog dialog = new OpenFileDialog();
dialog.Filter = "MicroStation DGN Files (.dgn)|*.dgn|AutoCAD Drawing Files (.dwg)|*.dwg|All Files (*.*)|*.*";
dialog.Multiselect = true;
if (dialog.ShowDialog() != DialogResult.OK)
    return;

foreach (string fileName in dialog.FileNames)
{
    mainAddin.Instance.App.OpenDesignFile(fileName, false, BCOM.MsdV7Action.Workmode);
}

If someone can reproduce this behaviour, its great. And if someone has a solution, it's even better.

Frode