Your company has two separate Python packages: 'app' and 'lib'. They are maintained by different teams. 'app' depends on 'lib', but 'lib' is still under development and its API changes frequently. To avoid breaking 'app', the team decides to use a virtual environment and install a specific version of 'lib'. However, during development, they need to test 'app' with the latest 'lib' changes from the Git repository. The current workflow is: (1) activate virtual env, (2) install 'lib' from local source using `pip install -e /path/to/lib`. This installs 'lib' as a development package. But one developer reports that after pulling latest 'lib' changes, importing 'lib' in 'app' still uses the old version even after re-running pip install -e. What is the most likely reason?