Assertion error from 'pip list' in virtualenv.

Assertion error from 'pip list' in virtualenv.

Pip list is throwing an Assertion error and I'm not sure how to resolve.
This has just happened after building 2 packages (PyUblas-2013.1 and
boost_1_54_0) from source. I am using virtualenv.
Error below;
(virtenv)[user@xyz ~]$ pip list
beautifulsoup4 (4.2.1)
biopython (1.61)
distribute (0.6.35)
methylpy (0.1.0)
MySQL-python (1.2.4)
numpy (1.7.1)
pip (1.4)
py (1.4.15)
pytest (2.3.5)
PyUblas (2013.1)
Exception:
Traceback (most recent call last):
File
"/home/user/virtenv/lib/python2.7/site-packages/pip/basecommand.py",
line 134, in main
status = self.run(options, args)
File
"/home/user/virtenv/lib/python2.7/site-packages/pip/commands/list.py",
line 80, in run
self.run_listing(options)
File
"/home/user/virtenv/lib/python2.7/site-packages/pip/commands/list.py",
line 127, in run_listing
self.output_package_listing(installed_packages)
File
"/home/user/virtenv/lib/python2.7/site-packages/pip/commands/list.py",
line 136, in output_package_listing
if dist_is_editable(dist):
File "/home/user/virtenv/lib/python2.7/site-packages/pip/util.py", line
347, in dist_is_editable
req = FrozenRequirement.from_dist(dist, [])
File "/home/user/virtenv/lib/python2.7/site-packages/pip/__init__.py",
line 194, in from_dist
assert len(specs) == 1 and specs[0][0] == '=='
AssertionError
Can anyone help me troubleshoot???
Thanks,