Navigation between Settings sub-pages takes several seconds

Steps to reproduce:
1. Go to Settings -> Inventory
2. Under Instances, click on Formats. A list of Formats is displayed in the right pane.
3. Leave the Formats page open and wait >1 minute.
...
4. Under instances, click on Contributor types

Expected result:
A list of Contributor types is instantly displayed in the right pane.

Actual result:
The list of formats continues to display for about 4 seconds, before being replaced by the list of Contributor types.

This is very slow, and even more confusing since the page doesn't clear while waiting. As a user, I could well assume that the values under Contributor types are the same as those under Formats, and move on before the actual list of Contributor types has finished loading.

If, after this, I continue navigating between Inventory settings, the pages load much faster, so it seems that the occasional slowness occurs after periods of inactivity.