Frozen Program After Invoking 'Destination File' Function
I just noticed this issue by chance, and have found it can be reproduced easily:
1- Open the program.
2- Add (replace if needed) a currently invalid (inexistent) drive path to the "Destination file" field.
3- Press the "Select destination file name" button.
The program will not open the expected window, and will start waiting indefinitely. Under that circumstance, it will be needed to close it forcibly.
The next time the program is opened, it won't matter if the "Destination file" field is empty or not, the issue will still happen in case it isn't changed to a currently valid path (entering the path with the keyboard).
I found this out when I used the program to multiplex a file to an external drive, extracted the drive and then tried to multiplex another one. MKVToolNix kept the external drive path in the "Destination file" field, but it wasn't valid anymore and it won't let me change it using the aforementioned button.