bxl-forever
OK, that’s a very common problem.  It comes from Nominatim, which is the name of the software used in that search box.  In a nutshell, it takes the closest match and returns the municipality where the first node of the street is located.  50% chances to be the one people expected.

https://nominatim.openstreetmap.org/ui/search.html?q=avenue+du+chili%2C+belgium

We have reported this issue several times but it has always been considered as of minor importance.

I added associatedStreet relations for both Brussels and Ixelles/Elsene for all those streets.  Let’s wait a couple more days to see if that makes a difference.