Resize image can choose zero size for small values

Latest Calibre on 18/02/12
calibre, version 0.8.40
Xubuntu with latest updates.
/usr/local/calibre$ uname -a
Linux bumble 3.0.0-16-generic #28-Ubuntu SMP Fri Jan 27 17:44:39 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

Input file is huge, so not attached. No output file, but I think the problem is obvious.

Converting PDF to EPUB fails.
Looks like there is no lower limit on shrinking images.
They do look like stranges sizes, but I didn't set them up.

From the log:
...
Rescaling image from 8x832 to 7x751 index-13_28.jpg
Rescaling image from 1296x2 to 566x0 index-83_44.jpg
Failed to rescale image
Traceback (most recent call last):
  File "site-packages/calibre/ebooks/oeb/transforms/rescale.py", line 54, in rescale
  File "site-packages/calibre/utils/magick/__init__.py", line 181, in fset
Exception: negative or zero image size `' @ error/resize.c/ResizeImage/2556

Rescaling image from 5005x4934 to 566x558 index-299_1.jpg
...