Patch: Replaced Command - Possess with 8 spell list

So the problem is with 2BAF and what it's actually looking at instead of what it should be looking at. 
Don't get me wrong, its a very interesting quick repair, I was never aware of that problem. Course as I said, it was a quick project either way so I'd have probably never caught it regardless. 

Yeah, the problem is that 2BAF (pending user command from battle menu) gets stale between the player readying the action and the player performing the action.  If it detects a different command, which it might if somebody else loads a menu, then the custom menu loads based on that information instead.  If it helps, it only seems to be a problem when both Tech and Magitek commands are in play on the player menu.
Could go about it by setting aside free workspace RAM for all of the actors, saving who has Magitek and who has Tech at the start of each battle (so that the value is fixed throughout the battle) and then determining which list to load based on actor position in that new RAM table.

...There's got to be a better way to put that.
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If you had 4 adjacent bytes of RAM (doesn't need to be SRAM), you might be able to run a check at the start of battle that records "This position has Tech" and "This position has Magitek".  Then, when deciding which list to load, you set X to the character position, convert that from a number to a bit position (so 0x08 becomes #4), and then load the RAM at that offset to decide.  ...Oh, wait, that would have the same problem, X as character position becomes a stale variable as soon as the action is readied.

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I'm not sure there's a good way to fix dynamic menu adjustment outside nailing it down before the battle begins, which means you can't have both in the same fight.  I don't think that will interfere with your plan to have optional magitek armor on the airship, because you'd set the status in an event, that'd set Magitek draw mode, and using that $6B4A for the list swap would then accurately prevent Magitek from randomly swapping to Tech mid-fight.