Because nobody else has reported about this issue, it is most likely caused by a plugin conflict. In my case the culprit was the Beta Tester plugin (http://wordpress.org/extend/plugins/wordpress-beta-tester/).
I found out that this plugin was causing the conflict by deactivating all plugins except for the Disable Updates plugin and then reactivating the other plugins one by one.
I think the only way to solve this is if you could do the same thing on your install.