Interesting - but agree, kind of like it.
If you want a more permanent solution to the error code Canon throws up when it goes hunting for a lens on the end of the chipped extender - use an M645-Nikon +(chipped) Nikon-EoS adapter. Works like a charm.
Thanks to a tip from James C, I use a couple of drops of 'fish glue' (a very old-school, very high-tack, very fast drying water soluble glue made from fish skins that was/is used in woodworking, especially veneer work) on the M645-Nikon adapter to ensure no mechanical slop between the two adapters.
The glue creates an easily removable but solid lock between the adapter + ___. Jim (and I) also uses it between any problematic adapters (rotational slop when focusing) and lenses. If I need to separate the pair for some reason, a good hard sharp twist and the two come apart with no fuss or muss and with just a quick 30 second cleanup with a damp rag. You can get it in (effectively) nail-polish (sized) bottles and one bottle will do for years as only use 2-3 drops on the odd occasion.