I'm not sure if this is a problem with the Backdrop site forum or with Backdrop, but when I try to create a new forum topic and hit "preview", I get an error along the lines of: The requested page "/node/preview/forum_topic/fede9ddc-85cf-45fc-9d00-ba8b04559a0f" could not be found. When I try to go back, the forum post text has been erased. This has happened a handful of times, in multiple different sub-forums.