Blanking bug's "Package"/"Project" field errantly selects "Distribution"/"Project"

[Matthew Paul Thomas]

1. Go to a bug report filed against a project, where you would like to move it to the package.
2. Expand the status row for the project.
3. Fill in the "Package" field.
4. Select the contents of the "Project" field and delete it.

What happens:
3. The "Distribution" radio button is automatically selected.
4. The "Project" field is selected once more.

What should happen:
4. The "Distribution" radio button remains selected.

The same happens when moving a bug report from a package to a project.

To fix this, change the code that selects the radio button when the corresponding field is edited. If the field contents becomes empty, *and* the other field is not empty, the other field's radio button should be selected.