When threads are merged, the singular thread should be searchable by all previous titles. This doesn't appear to be the case. For instance, if threads 2 and 3 are merged to thread 1, thread 1 can be found by searching for the title of 2 or 3.
Example: Searching "once per page refresh" should surface this issue, because it contains a merged thread under the same name.
Merged 2 posts from UBlock Origin element picker only works once per page refresh.