Half of the labels disappeared

[Dark Waves]

Last night I finished adding the last couple of labels, saved them, then scrolled through the list, but midway through the alphabet (sometimes MAC, sometimes Mixer) all following slots were blank: no user created, no factory ones.  The longer I scrolled clockwise, the longer it would take to return to visible entries, so it seems there were just blank slots there.  Power cycling the unit a few times did not resolve the disappearance of the missing items, which included a bunch I had made the previous day.  However, ones in the first half of the alphabet, both custom and factory, are still there.  OS is 1.1.020.