I tried to open many files during my previous working session with IMatch and got mistakes for every file I tried to open.
After rebooting PC I have read your message, started IMatch and couldn't reproduce that bug. And yes, every time I am starting import now, I see that "File name" field has file name. So maybe problem has disappeared after restarting IMatch, who knows. If I get this mistake one more time, I will let you know.