Affects back to 2.0 (when keyword args were introduced),
so this doesn't seem to be an optimization bug introduced in 2.1/2.2

I'm actually not sure about the specs and if there's some special case
for kwargs interacting with aref/aset...

For instance, frequently use the 'sequel' API to write stuff like:

   DB[:tbl][id: 123]

(I've been doing this since before keyword args were introduced)