Why do I get an error in the second case, when it's the same thing except using an anonymous array rather than a named one?

Pike v7.7 release 13 running Hilfe v3.5 (Incremental Pike Frontend)

array a = ({ "hello world" }); Regexp(a[*]);

(1) Result: ({ /* 1 element */ Regexp.SimpleRegexp(hello world) })

Regexp(({"hello world"})[*]);

Compiler Error: 1:[*] not supported here.