Reactions indications are inverted

This is intentional and matches Discord's current tooltip, which uses the identical phrasing. You're right that it bends standard grammar: "react" is classically intransitive, so it shouldn't passivise. But messaging platforms have coined a transitive sense, "to react an emoji onto a message", and under that reading " reacted by Hampus" is simply a clipped passive: " [was] reacted by Hampus." The ordering is deliberate. In a tooltip anchored to an emoji, the emoji is the topic. It is the thing you hovered over, so it belongs in first position, directly beside its large preview, with the attribution following. Fronting the names ("Hampus reacted with ") would be cleaner grammar but worse information design: the tooltip would open with data you didn't ask about and bury the element it's describing. Topic first, detail second is the logical structure here, and slight ungrammaticality is a small price to pay, I think. Closing as working as intended, since it follows the convention users already recognise!