On Select topic you can only choose a few things and then there is a field with your own input.
For example I wanted to post something funny. I did not know, that there is already a topic "funny" and just wrote "fun". Now its shown on a different topic. That could be better. Why not implement a search dropdown field for all topics. With the amount of posts in brackets would be even nicer.
Also its not possible to change the topic later on edit, or did I miss anything?