Same Problem here with 4.2.8 and 4.2.9 on Windows XP SP3.
Symptoms are the same as in
https://winscp.net/forum/viewtopic.php?t=8876
https://winscp.net/forum/viewtopic.php?t=8901
https://winscp.net/forum/viewtopic.php?t=3732
Unmounting all network drives seems to solve it and the explorer view is not affected. I also can't reproduce it on Windows 7, just XP
Can you send me an email, so I can send you back a debug version of WinSCP to track the problem? Please include link back to this topic in your email. Also note in this topic that you have sent the email. Thanks.
You will find my address (if you log in) in my forum profile.