The comma between city & state in contact addresses is being stripped out

I noticed that for all of my contacts (which are syncing with Gmail), the comma between city and state is missing. If I edit a contact’s address and add the comma manually, the Address Details editor window pops open. If I hit OK, the comma disappears again.

With the comma missing, my contact addresses look like this:

Street Name

City Name State Zip

Instead of the common layout (at least in the US):

Street Name

City Name, State Zip