Strange issue with Editors, but not Administrators

My sites recently changed to a new server with the same host, but in the transfer some things got changed. For the most part, everything on the sites seems to be back to normal, but there is a problem on one site.

On all my sites I have and Administrator user and an Editor user. As much as possible I try to do all posting as an Editor, and only use the Administrator role when I have admin tasks (such as updating WP, adding plugins, etc). On one site that got moved, when logged in as an Editor, I get a download post.php or post-new.php box whenever I try to add a new post or edit an old one. However, this doesn’t happen when I try the same thing as an Administrator, and it doesn’t happen to my other sites on the same server.

I ‘promoted’ the Editor user to Administrator, and everything works fine, but it’s not a satisfactory fix because I like the idea that the admin role should be used rarely.

Because it doesn’t happen on the other sites on the same server, I don’t think this is a server issue, but I chmod-ed the directories to 755 and files to 644 just to be sure. However, it didn’t fix the issue.

Any suggestions would be appreciated.