The interesting bit is that the cell in frame #1 and #30 are different. The
method description only gets called if the formatter of a cell is nil. This
means, the second cell doesn't know about your special formatter, which results
in the wrong display. But why are there two separate cells involved and why
doesn't the second one have a formatter?
OK, I just found the teason for the later, there is a copy and paste error in
the copyWithZone: method of NSCell, which I am going to fix now. Maybe this
resolves your issue.