05-25-2016, 12:09 PM
Interesting. I imagine this is because it uses JavaScript to determine what post it's interacting with. It likely wasn't written well and stores the post ID in a single variable, overwriting it with each new thanked post. A refresh fixes this and that's about all I can really recommend at the moment as it's a third-party plugin that provides the feature and it will be built-in come the new version of the MyBB software. Thanks for letting us know though!