Well, I believe I have some idea on why that happens (not the romhacking reason, but more of a "understanding the battle engine" reason.
There's a major actual difference between how Hide operates in the SNES version than in the GBA version.
SNES:
This is what I wrote about this in a Gamefaqs post.. since analyzing and thinking about it:
http://www.gamefaqs.com/boards/genmessage.php?board=929937&topic=44525287&page=2When Edward is critical (which is a hidden status), a Hide command is issued immedately after the status change (Hide is also another special hidden status). If you are fortunate, you can queue in something (particularly healing) before that "auto-Hide" command issue even occurs. Fortunately.. Edward's not on the team long enough to expose any real bugs (if any).
GBA:
When Edward is critical, a Hide command is issued WHEN his "logical" turn would have occured (in other words, instead of getting a menu to input the next command, he is auto-issued a Hide command). There's a conflict of status that is happening.. the Hide and Berserk status.. Berserk demands on each turn that the character attacks. Hide well, makes him "invisible" (like how Jump does) so spells and attacks can't occur.
Hide status seems to be removed somewhere along this process when everyone else is dead... it seems to be removed right after the first attack (after everyone has died)... although technically it is after the failed counter attack (if there is one by the enemy, I tested this against a Behemoth so my analysis could be off, but I feel I'm pretty sure of this, I should probably test against that boss monster to be sure). Then Edward becomes vulnerable again...
Edit: There are edits since the Gamefaqs board has no edit button.
We have EVEN MORE themes now, but some old ones are gone...