In Evolution 2.24, go:
* File -> New -> Contact, and click the "Mailing address" tab
* Click in one of the "address" fields, to make it active.
* Press tab repeatedly, and observe that the tabbing order is: Address, City, Post Code, State, PO Box, Country.

Objection:
The "PO Box" field feels out-of-place between "state" and "country" in the tabbing order. I'm also slightly unsure if it's needed as a field.

Suggestions:
* (less intrusive) Could the tabbing order please be: Address, City, Post Code, State, Country, PO Box (this option assumes that PO Boxes are infrequently used as a separate field, which is certainly the case for my contacts); or Address, PO Box, City, Post Code, State, Country (possibly the more logical order, but for people who don't use this field likely to be just as annoying).
* (more intrusive) Does "PO Box" really need to be a separate field? Can't the user just put "PO Box 2741" or whatever in the "Address" field? It only seems to make sense in situations where someone has a street address and a PO Box address, both in the same suburb & post code, and you know both, and you use both, and they are both work/home/other addresses. One possible more powerful arrangement would be make the "Home", "work" and "other" labels/sections into selection/option boxes, in the same way that Work/home/other are options for a contact's email address in the "contact" tab. That way the user could have two home/work/other addresses for a contact (one the PO Box, one the street address), and thus the PO Box field is no longer needed.