My example is django. To reproduce:
1. Install django 1.2.5 from ubuntu natty repository (/usr/lib/pymodules/python2.7/django).
2. Install django 1.3 from djangoproject.org using tarball and setup.py using defaults (/usr/local/lib/python2.7/dist-packages/django)
3. Install Eclipse IDE for C/C++ Developers, Version: Indigo Release.
4. Install pydev 2.2.2 release using Help > Install New Software... from http://pydev.org/updates
5. Autoconfigure python 2.7 interpreter, note /usr/local/lib/python2.7/dist-packages preceding /usr/lib/pymodules/python2.7 in System PYTHONPATH list.
6. Create new django project.
7. Create application in django project using right-click in package explorer > Django > Create Application.
8. Edit models.py and add the following line:
from django.shortcuts import re
(9. note that pydev offers to import "return" :-)
10. hit ctrl-space to see code completions, note absence of django 1.3 function "render".
11. type out "render" manually.
12. hit F9 to run models.py. Note absence of errors.
This may or may not be related to Bug ID: 297191: "PYTHONPATH magically ordered leading to wrong version errors". I would have added to that but I couldn't figure out how to reopen it. Link: http://sourceforge.net/tracker/?func=detail&aid=2971918&group_id=85796&atid=577329
Whoops, forgot to add that uninstalling django1.2.5 and rebuilding the interpreter paths (by clicking Apply in interpreter preferences) makes "render" show up again in code completion.
And as always, thank you Fabio for all your hard work on pydev!