There seems to be a bug in Topic subscriptions (cf. T263821):

I’ve made an edit request in Commons for gadget LargerGallery with caption Necessary update after change in code base and after creation hit the subscribe topic button.
Then, since it’s the same cause and almost the same fix, I went to the yet unexisting talk page for gadget DeferredDisplay, copy-pasted the content from LargerGallery request and adjusted for the other gadget. This means the caption is the same: Necessary update after change in code base.

After saving I was very surprised that this section was already displayed as being marked as topic subscribed. So, I opened Special:TopicSubscriptions only to see the subscription for the section in LargerGallery, nothing for the one in DeferredDisplay. And after I unsubscribed in DeferredDisplay (hit the button to the right of the caption) the subscription for LargerGallery was removed.

Of course, I would expect that this does not happen and both topics are distinguished despite the identical caption.