hg convert hangs in toposort()

[Frank Kingswood]

Hallo!

I'm experiencing hangs in converting a CVS tree, in calls to toposort(), 
in particular the while loop which starts at line 129 in
http://hg.intevation.org/mercurial/crew-stable/file/6605a03cbf87/hgext/convert/convcmd.py

The state alternates between
visit=['3', '4']
removed={'1': 1, '2': 1, '5': 1, '7': 1, '6': 1, '9': 1, '8': 1} 
parents={'1': [], '3': ['3'], '2': ['1'], '5': ['1'], '4': ['3'], '7': 
['6'], '6': ['5'], '9': ['8'], '8': ['7']}
self.map={}

and

visit=['4', '3']

(with the other variables unchanged).

It is not entirely clear to me what the expected behaviour of toposort 
is, can anyone shed any light on this problem?

This is with version 0.9.5 (as packaged in Debian), but the toposort() 
code is identical to the current crew-stable tree.

Frank