Cannot check for updates via Windows 8 when using HTTP proxy

WinSCP 5.5.3 on Windows 8.1 Pro

If I have my HTTP proxy configured in Internet Options, checking for new updates produces the following error:

Couldn't resolve hostname http=proxyserverhostname:3138;https=proxyserverhostname:3138;ftp=proxyserverhostname

Where proxyserverhostname is the hostname of my proxy (I redacted it) and 3138 is the proxy port.

All other functionality works fine.

Thanks for your report.
I have sent you an email with a debug version of WinSCP to address you have used to register on this forum.

Check your mail, I just sent you some debug logs.

This bug has been added to the tracker:
https://winscp.net/tracker/1171