Yeah - the melding interface is poor-piss designed - I've actually end up moving the item(s) I want to meld (multiply times or with overmelds) from armory to inventory and also keep only keep there only those materias need for that particualr meld to avoid repeated scroll accross long lists of items and / or materias and most of all melding something incorrectly. Game should also STAY in the melding window in case of the failed meld to alow you to perform another attempt right away as long as you have the same materia and catalyst still available.