Noticed this happening on 1.54 and also 1.56. Hitting the 'post reply' button after typing a reply nothing happens, it hangs in edit mode, but when I look at the thread, the reply is posted. Encourages multiple attempts to post and duplicate content.
If it's just a "little slower" here, then that could be down to all sorts of environmental factors really. The button re-enabling is simply time dependent. A slower connection could make this more visible.
If it's actually not appearing on your local site until a refresh, this is very likely down to a customization. That said, as usual, network issues can cause all sorts of weird behaviors.
I assume this is specific to you. Anyone else seen this sort of behavior?