It's not possible to filter in the grid on multiple conditions. I don't know or it's a bug but in an earlier GUI version I thought this was possible. When I try to filter in a grid by more than one filter condition the first condition is switched off. 

For example:

I would like to search all articles with the material "HDPE" and the colour "Blue 1% (1)”. My first filter condition is material "HDPE”. 

As second filtering condition I choose colour "Blue 1% (1)”. I expected all rows with both of these conditions. Instead of combining these conditions, the first condition is overwritten with the colour filter. 

Filtering not by the column header but from the Filtering pop-up or the Quick filter the system gives the expected result.