Note: I've made changes to the combatant status and class status development values, so numbers will be different than screenshots above, but fundamental problem persists.
I can confirm Delete is disabled when the player leaves my party. See below but does not appear to be related.
I've been trying to dig into this and it appears changing the classes works fine until I save the game and load from that save file. Once the save file is loaded, the combatant's stats largely match the combatant + class stat values, except for an extra 2 points in ATK which the class status development does not contribute. I can reproduce this as the class levels up if I save and reload the class's status development appears to get saved to the combatant itself, and changing the class has no effect (except for ATK).
Combatant status + Class status development values
Class level 3
Max HP: 90 + 5 = 95
Max AP: 8 + 1 = 9
ATK: 14 + 0 = 14 (but displayed as 16)
STR: 16 + 1 = 17
INT: 12 + 0 = 12
SPD: 15 + 3 = 18
When I switch between classes I expect to see the combatant's status values updated relative the class level and status development, however actual behaviour is only the attack stat changes by 2 points, which looks like was increased at class level 3 even though the status development does not specify any increase (only 1point at level 5).
I'm not sure what's going on, but it seems like the class's status development values are getting saved onto the combatant itself. I don't where the extra 2 ATK is coming from.
Any idea what might be causing this? Also is there a way to log the class status values so I can verify what the game thinks is the combatant's vs class status values?
Please let me know what I can do to help get to the bottom of this. Appreciate your help.