Cannot attach files in forum until post Previewed

I may be wrong, but it seems that you sometimes cannot attach files to a post until after you press Preview. This is confusing and offputting.
For instance, I just tried to post in Show Us Your Creations and couldn't see the Attach part of the form until I did a Preview. But right now I can see it on my screen under this post I am typing.

This seems to be working fine now. Either it's been fixed or it was a random event.