for information, version 4.7.3
some cities, like vienna, are very densely populated. In vienna are are added to the usualy address-data (name, street, housenumber) furthermore stair-number or door / top-number. The latter, I think, would be appear in each bigger city. In vienna you write an address with following syntax: 

name, street, house number / stair number (opt) / top number, zip location (town, city) 

Expl: Bernd Mullet, Fugbachgasse 21 / 1 / 12, 1020 Wien 

If you deliver it to open streetmap there are problems. It can't found an adress like 

Fugbachgasse 21 / Wien, [1,1020] 

you have to change to 

Fugbachgasse 21 Wien, [1020] 

I think, you will find a genius solution, like mostly in the past ;) 

LG, Bernd