What's this? Why is case 2 different from the other three?

Pike v7.3 release 62 running Hilfe v3.5 (Incremental Pike Frontend)

function plus = `+; `+(("hello world"/" ")[*]);

(1) Result: ({ /* 2 elements */ "hello", "world" })

plus(("hello world"/" ")[*]);

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

array(string) hi = "hello world"/" "; `+(hi[*]);

(2) Result: ({ /* 2 elements */ "hello", "world" })

plus(hi[*]);

(3) Result: ({ /* 2 elements */ "hello", "world" })