Hi Pete,
Yep. Log back into the account where you're having trouble. Go to your home folder. Then, go to: Library > Safari. Delete everything in that folder except the "bookmarks.plist" file. Do this while Safari is NOT running.
Next, go to your home folder and then Library > Preferences. File the file called "com.apple.Safari.plist" and trash that as well.
Once you've done that, open Safari. You'll notice that it's reverted back to default settings. You'll need to go back and set all your preferences again, but hopefully this will solve the downloading problem.