When adding a relationship, the order of the entities changes for no apparent reason, e.g. in the relationship editor:

Adding a release-level relationship, the order is:

• recording
• place
• label
• area
• series
• artist
• release

Adding a release-group-level relationship, the order is:

• place
• release group
• artist
• series

Adding a recording-level relationship, the order is:

• release
• label
• area
• artist
• work
• recording
• place
• series

Regardless of which one is selected by default, I think the order should be consistent, so that it's predictable.