Tried both stable and beta versions. I think windows doesn't fully load that extension or something like that. When I do "regsvr32 Dragext.dll" it says extension is loaded, but the problem still exists. Tried to unregister->reboot->register->reboot... nothing.
Under uncertain conditions it really DOES work, after long standby (> 10h), sometimes not. But it works only until the first reboot|logout.
After all WinSCP is a really good piece of software, thanks.