Canna is hosed wrt Backspace and Delete keysyms

[21.0.67 and 21.2.13 behave identically.] Hitting either Backspace or Delete in Canna fence mode yields: Signaling: (wrong-type-argument characterp nil) canna-key-proc(nil) canna:functional-insert-command2(nil 1) byte-code("..." [nil ch char-or-char-int-p arg last-command-char event-to-character last-command-event canna:functional-insert-command2] 3) canna-functional-insert-command(1) call-interactively(canna-functional-insert-command) The only way to delete backwards in fence mode is to type an explicit [(control h)]. This is one of the worst of all possible worlds. What is (event-to-character event) supposed to return when `event' is #<keypress-event backspace> or #<keypress-event delete>?