Modal dialogs vanish

All modal dialogs in Winscp (delete files, overwrite files, exit app) are vanishing as soon as they appear, with the default action (cancel). I can get around this by disabling the dialogs, but i would prefer they actually appear.
This started randomly whilst using 4.0.5, and updating to 4.0.7 did not solve my problem.
I assume this means something on my computer is causing it, but i cant think of anything.

Sorry, forgot to add i'm using Norton Commander interface on XP.

I have never seen the problem before. Does it happen with any dialog? Or just message boxes?

It just seems to be dialogs that have multiple options, and require input.
Also, it only appears on one of my connections, an SFTP to a remote server using a private key.
FTP, and SFTP using a password work without error.

Can you provide me your email address, so I can send you a debug version of WinSCP to track the problem? If you do not want to post the address here, you can send me an email. You will find it (if you log in) in my forum profile. Thanks.