Yeah, that was my thread (https://forum.pfsense.org/index.php?topic=102069.0). I'm interested to see what comes of this too. Although ssh and logging in to the pfSense box itself are workarounds, using the GUI would still be easier and there is no reason why that shouldn't work as epected.
I too had thought it was the size of the file, but there may well be something else going on, or more than one issue. Either way, the "Edit File" and "Filer" functions don't seem to function as well as they might.