image status report is unreliable

I'm setting up a new site with the latest alpha.

On the site status report page, image module reported the images folder as missing.
But I could see it in FTP. I tried setting the permissions, and so on.
Visiting image settings page got me a message that the images/temp folder had been created.
Yet the status report still showed the error!

I had set the site up with a brain transplant from my development site, so the system's file_directory_temp was wrong. I deleted this system variable, deleted the files folder, went back to the core files admin page and got an error there: as expected.

I have now created the files folder from scratch. A visit to the status report page creates the images folder for me.

I think the problem was that the files folder had no htaccess the first time (probably because of the brain transplant -- I made the files folder myself, and Drupal thought it was already made too, so didn't put the htaccess in). At least, that's the only difference I can see.

I've seen a few forum posts about 'directory missing' errors for image module -- perhaps this is the problem?