NSCell won't remove from NSTableView

I have an NSTableView filled with custom NSCells. Most include text, but one contains an NSButton. When I reduce the amount of objects in my data source,开发者_运维问答 call -noteNumberOfRowsChanged and -reloadData, all the NSCells with text disappear, but the one with the button stays there.

What additional work do I have to do in order to remove this last NSCell from my table?