Assigning Materials to elements
Hello, I have a question regarding materials. I know that I have to add and create (IFC) materials in the Materials Tab 
I can then add this material to a certain wall for example, when I click on Scene -> Geometry and Materials 
The only question is: why can I choose more than one material in the Scene/Geometry and Materials Tab (in this case brick and mineralwool) but it doesn't show in the wall properties in the outliner? 
When I choose more than one material in the Materials Tab it shows in the outliner but as soon as I save the IFC file and reopen it, the wall is only made from brick again. (And yes, the Mineralwool I am using as second material is saved as an IFC material).
Is that a bug? Or am I doing something wrong or forgetting something ovious? Thanks already!
(I am using Blender 3.6 and the BIM Add-on v0.0.240317)