I use the RadOpenFileDialog with the MultiSelect property set to True. My test folder contains 105 files with sizes about 1 to 2 kb and all the same extension. If I select multiple files with <ctrl>+<mouse left> the selection behaves as expected. If I select multiple files with <shift>+<mouse left> I have to wait al long time. Unselecting the file by clicking on an unselected entry is also very slow. If I try to select all files with <ctrl>+<A> the dialog remains busy and does not respond anymore.
My code for testing is as simple as this:
private static void TestFileOpenDialog()
{
RadOpenFileDialog dlg = new RadOpenFileDialog();
dlg.InitialDirectory = @"path to files"; // 105 files with sizes from 1 to 2 kb
dlg.Filter = "my files (*.mal)|.mal";
dlg.FilterIndex = 0;
dlg.MultiSelect = true;
DialogResult result = dlg.ShowDialog();
}