unexpected space insertion (related to unusual unicode characters ?)

When I type this in the editor:

```clojure
(ℕ-blabla 42)
```

`clojure-mode` automatically inserts a space, yielding:

```clojure
(ℕ -blabla 42)
```
(this does not occur if I replace `ℕ` by e.g. `N`) 