Have a newly installed Studio, and no Titanium SDK.
- Install an SDK via the "Install Specific Titanium SDK..." menu, or via the Studio prompt to install on startup.
- Let the Studio complete the installation.
- Click to create a new Mobile project.
Notice that the Titanium SDK version drop-down is empty.
Restarting the Studio fixes the problem.
This issue does not effect versions where there is already (at least) one SDK version installed.