First post disapproval on the default custom reason seems to be broken on 3.0.8 unless you write something to the comment box.

Steps to reproduce,
Open a post with something on queue -> Click the "waiting for approval" link -> select disapprove -> from the drop down box select "The reported message does not fit into any other category, please use the further information field."
Hit submit and you are instantly redirected to MCP and the post appears to be rejected.
It is not on the list.

However, when you go back to the forums you see that the post is still there.

Workaround,
Type something to the field and submit.