See comment here: #556 (comment)

merge(["1"], {a: 2}) gives a different result than merge({x: ["1"]}, {x: {a: 2}}).x, which is probably unexpected.

Note that the merging is consistent in the compat version.

The type checking performed on each property should possibly instead be done to at the top level of "source" and "target", in order to keep the recursive behavior consistent.