currentTiddler in function - Is this odd or am I missing something?

Folks,

to solve this issue;

I wrote a function as follows;

\function pretty.permalink() [<open-sq>] [<currentTiddler>] [<close-sq>] [[(]] [{$:/info/url/full}] [[#]] [<currentTiddler>] [[)]]  +[join[]]
\define open-sq() [
\define close-sq() ]

<<pretty.permalink>>

I dont understand the result;

[](file:///I:////!Master/KeyWikis/BlogToSelf.html#New Blog Tiddler 13)

Why does the [] not contain the current tiddler?

Even this simple form

\function pretty.permalink() [<currentTiddler>] [[something]] [<currentTiddler>] +[join[]]

<<pretty.permalink>>

Fails with the first use of [<currentTiddler>] not being returned.

Tested in TW 5.3.7, 5.3.8 and 5.4.0-prerelease now