WinSCP: annoying black regions when moving the sliding bars

I have tested Winscp (an open source ftp / sftp client) 5.7.7 from

https://winscp.net/eng/download.php

As you can see in my screen-shot, annoying black regions appear when moving the sliding bars, which make the program difficult to use since you cannot see the files names! (probably due to refreshing problems)

r71519
Testing environment: Virtualbox 5.0.20 on Debian jessie
conectting to my host by sftp