So the "New post" button while reading a thread is seemingly broken (or at least seem illogical) - it starts a new thread in the current forum instead of adding a new post to the current thread.
Guess someone will either have to remove the button from the page template, change the text to "Create new thread" or change what function is called when the button is clicked, so a new post is added to the thread instead of a new thread to the forum.
On to the next test.
Second post in thread - testing delete
Yep - delete post (icon in lower left corner of post) is only available when the thread just consists of one post (your own). As soon as you (or anyone else) adds a second post - which references the first post, deletion is deactivated. From an end user perspective, the tool tip really ought to have been labelled "delete this new thread" instead of "delete post".
I assume the features works more fully for moderators - who probably can nuke sub-threads in a thread - i.e. a post and posts that refer to that post - to preserve database consistency (no posts with "reply-to" references to posts no longer there).