Sometimes -- and I can't reproduce this -- fn+delete *shows* no deletions, at least not at first. But after I arrow up or arrow down, the deletions show. Weird!
Sorry, but I don't know how to reproduce it. It was happening in a .rb file in the right column with a two column layout. After I opened a new file and returned to the .rb file, it worked fine.
(Obvious background for Mac apps: "delete" removes the character to the left of the caret. "fn+delete" deletes the character to the right of the caret.)