Upgrade to 6.3.7 is the official answer, but if you have a look in the comments, you'll see a link to a new .jar you can download.
Download it, then use the plugin manager to "upload plugin". I would keep a copy of the .jar from your current installation just in case, but I'm always cautious.
No and yes. You do not need to worry about it appearing in the "wrong" list on your current installation. Technically, it is a user-installed plugin because you did it by hand, but the difference between system and user plugins is not much more than "it came in the installation off-the-shelf" However, before you upgrade, you must remember to remove it, or it may interfere with the (fixed) new version in the new installation.
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