Ok, I deinstalled ZoneAlarm (it started to piss me off) thus fixing my firewall problem. And now my computer doesn't hangup each time i change the task anymore! Must have been a problem with zonealarm, thanks anyways for your interest in fixing this :-)

It does not happen when WinSCP is idle so unfortunately i can't repeat it at the moment 8[ (i've got some problems with my firewall... -.-)

I'll post as soon as I fixed this problem 8[

Does it hang, when transfer is in progress or even when WinSCP is idle? Can I have an email contact to you, so I can send you a debug version?

The program works fine and downloads at full speed while it is in the background or while it is in the foreground. Just when i try to change the task (e.g. after telling the program which file to copy, I change the task to firefox to browse the net) my computer hangs up for like 30sec just to recover again.
This works both way (WinSCP --> other task or other task --> WinSCP) but does not interfere with the file transfer. Any ideas why this could be?