I have an interesting issue with the server on any Win7 machines where the dungeon walls and wilderness mountains don't display. Essentially, anything of that dark grey color is just a blank space. Has anyone else encountered this issue?

I run putty across all my machines, with the settings to the standard for the server.
It works just fine on my laptop that uses Ubuntu, and also OK on the one with WinXP. I can even get it to display okay on my Samsung Galaxy S3 w/ Connectbot as the SSH client. It seems to be a Win7 isolated issue.