That West Berlin was an enclave deep within GDR, completely encircled by the Berlin wall. For some reason I thought that Berlin was right at the border between FRG and GDR with the wall splitting it in half.

Multiselect lists are outdated design, requiring prior knowledge of what they are and the use of keyboard (that you might not have if using a touchscreen device) for a simple interaction with a webpage is terrible UX. The issue is that it’s how browsers render them by default, a ‘proper’ multiselect requires a bunch of css and javascript.