Which is totally ok!
Although I would either be slighty confused by it or more likely wouldn't even register it at all, as not expecting thanks to be directed at me.
After all, placing the divider is somewhat of a selfish action on my part, omitting later stress...

That's one of the exceptions I was thinking about. Looking at someone and deciding to do something beneficial specifically for that person.

Home Bargains is British, isn't it?
So maybe region-dependent custom.
Here in Germany I would judge it to be equally uncommon both in cities and the more rural areas.