Zip code field does not (re-)appear when switching from e.g. "Tonga" to "Germany" but is required

Problem / How to reproduce:
When switching to for example "Tonga" (a country without zip code field) first and then switching to "Germany", the "Postleitzahl" (zip code) field does not appear in the form again. On submit an error appears because the "Postleitzahl" (zip code) is required for Germany.

A little help:
There are NO JS Errors and the spinner loads correctly. So it seems like a logical problem.