Version: (using Devel) OS: MS Windows Installed from: Compiled sources When leaving fields empty on the "change votes" page, the bug tracker returns a page which says that "Only use non-negative numbers for your bug votes.". This is misleading. I'd expect it to treat empty fields as zeros.
This problem still exists on the current version of the site.
This would need to be fixed upstream in Bugzilla itself; please report there if it's something you're still interested in. Thanks!