Currently all properties on Immoweb show prices excluding taxes (even for rental properties and properties that aren't new constructions).
We have already contacted Immoweb and we are communicating with them to solve this as quickly as possible !
We will keep you up to date and we will notify you once it has been fixed.
Note that we aren't the only software experiencing this, all Zabun and Skarabee publications have the same issue for the moment.