Byte-compiling ibuf-ext.el currently emits the following warning:

  In ibuffer-diff-buffer-with-file-1:
  ibuf-ext.el:1660:8: Warning: ‘unwind-protect’ without unwind forms

Trying out ibuffer-diff-with-file, I also see some undesirable
behaviour:

0. emacs -Q
1. M-x find-library RET ibuf-ext RET
2. C-o
3. M-x find-library RET ibuffer RET
4. C-o
5. M-x ibuffer RET
6. * u =

The resulting *Ibuffer Diff* buffer opens with two empty lines and point
on the second, and closes with two 'Diff finished' sentinel lines.

The attached patch fixes these issues, bringing ibuffer-diff-with-file
more in line with its apparent inspiration, diff-buffer-with-file.

WDYT?

BTW, just curious: why is diff-command called through the shell in
diff-no-select (and ibuffer-diff-with-file), rather than directly?

Thanks,

-- 
Basil