I noticed it hours ago, so I haven't do some experiments about it.
But after I close WinSCP and restart with the same SSH connection configuration, only one port is bounded now.
My usage is usual. Only operations are changing/refreshing local/remote working directories in explorer view and uploading/downloading files (cancelled sometimes).
I think the problem comes from time. I use WinSCP in my working environment, so the connection will be kept for weeks until my local machine has to close.
I also met the same problem months ago, but I didn't check it with netstat.
Status of these ports are all "bound" but not listening or in a connection. It looks like something like memory leak.
I will keep observing ports in following days.
Thanks for you report.
Can you tall what operation causes an additional port to be bound?
Are you using some unusual settings? Like SSH tunneling?