to reproduce:

(package-initialize)
(require 'evil)
(setq testmap (make-sparse-keymap))
(define-key testmap (kbd "SPC") #'test)
(evil-define-key 'motion global-map (kbd "SPC") testmap)
(evil-mode)
(describe-keymap global-map)

This appears to be caused by keymap.c line 3313
SYMBOL_NAME (shadowed_by)
where shadowed_by don't have to be a symbol (In this case its a keymap)