Strange reaction to the numbers.
If the name of the topic have numbers.
This guy had the same issue about write-api: https://community.nodebb.org/topic/9966/cannot-find-installed-plugins
It's not possible to do exactly what you say, but it is possible to accomplish a similar thing by creating a NodeBB plugin which implements the API endpoint you want, instead of using the built-in API.
This is working as intended: in NodeBB we define your "topic post" (OP) as a post in itself as well.
I know some forums treat topic posts as a separate entity but I think this method makes more sense
Ahh yeah that's a bit confusing, the merge topic tool can be used between categories, so you should click merge first and then select the topics. The placement seems like a theme/skin issue.