Steps to reproduce:

1. Launch Hob
2. Select a machine (e.g. atom-pc)
3. Select a base image (e.g. core-image-minimal)
4. Open the Advanced configuration dialog and in the 'Image types' tab change your distro selection (e.g. to poky-tiny). Save your changes.
5. When the recipe parsing completes, open the 'Select a base image' drop down menu

Outcome:

Between the options listed in the drop down menu, you'll see the 'select a base image' one. This should not show, since a base image (core-image-minimal) was already selected. If you choose the 'select a base image' option, the interface becomes inactive and shows a spinning cursor indefinitely. 

Expected outcome:

The 'select a base image' option should not show in the drop down menu once a base image has been selected.