Unable to reproduce internally.
The user is unable to expand the class dialog menu when creating a new blueprint class on his Mac. He provides a video showing the issue he is experiencing in 4.7.5 as well as how it works correctly in 4.6.1.
1. Create a new Empty BP Project
2. In the Content Browser use 'Add New' button and create a new Blueprint Class.
3. Attempt to expand the 'All Classes' menu.
Head over to the existing Questions & Answers thread and let us know what's up.