cubicweb #344258 workflow image generation is broken [rejected]

When I go to the workflow view of Version, no more image is generated (https://www.logilab.net/extranet/cwetype/Version?vid=workflow). However it seems to work for the other entities.

Here is the traceback:

$ tail /var/log/cubicweb/extranet-jpl-all-in-one.log
    view_func(**context)
  File "/usr/lib/python2.5/site-packages/cubicweb/web/views/basetemplates.py", line 92, in call
    view.render()
  File "/usr/lib/python2.5/site-packages/cubicweb/view.py", line 148, in render
    view_func(**context)
  File "/usr/lib/python2.5/site-packages/cubicweb/web/views/__init__.py", line 102, in call
    self.cell_call()
  File "/usr/lib/python2.5/site-packages/cubicweb/web/views/__init__.py", line 111, in cell_call
    os.unlink(tmpfile)
OSError: [Errno 2] No such file or directory: '/tmp/tmpsHKiaA.png
priorityimportant
typebug
done in3.3.3
load0.200
load left0.000
closed by<not specified>