Strange formatting of optional Scheme function arguments

[Werner LEMBERG]

With current git (commit 44f1033467a6, using Guile 2.2.7), the
formatting of optional Scheme function arguments in the IR looks
strange.  For example, the signature

```
(define*-public (markup->string m #:key (layout #f) (props '()))
```

appears as

```
Function: markup->string m #:#:layout #:#:props
```

Any idea how to fix and/or improve this?  Shall I open an issue?


    Werner