Emacs hangs in `let`, `loop` form

This happens always at the end of file. When I write

```
(let [a 10]
```

or

```
(loop [a 10]
```

then hit enter key, emacs hangs. The CPU usage of Emacs process hits 100%. This problem does not happen when I write the code in the middle of file.

This seems irrelevant to cider or nrepl.

OS: Mac OS X 10.11
Emacs version: 24.5.1
clojure-mode (version 4.2.0-snapshot)  ;; 20151001.2255
