GravityForms post creation without category or custom fields? Blog
Having your GravityForms producing posts? We found out the other day the using caching plugins such as DB Cache Reloaded ( http://www.poradnik-webmastera.com/projekty/db_cache_reloaded/ ) removed all custom field input as well as setting the category to default.
So .. if you have strange behaviour all of a sudden.. try to disable some plugins at a time and see what happens.