An array variable created by export/readonly builtins inside a function becomes a locale variable to that function unexpectedly

[ziyunfei]

$ ksh -c 'foo() { readonly a=(1);echo a=$a; }; foo; echo a=$a'
a=1
a=1
$ bash -c 'foo() { readonly a=(1);echo a=$a; }; foo; echo a=$a' # a becomes a 
local variable
a=1
a=