I... posted a bug report on the Steam forums, not knowing about this spot. (Also, would've likely bought it here if I knew about this spot!)
(It... had to do with *something* related to the Scarecrow Status causing characters to restore 25 HP every time they hit, and also disappear entirely except as inventory items if they became Onaholes)
EDIT: I've... also been completely unable to find the Blue Jewel from the hint offered shortly before you get the Blue Tome.