Mass property input in custom sections - Multiframe


I'm using Multiframe v8i (version 15.04) and I would like to run a self-weight analysis using custom (User Defined) sections.

The problem is that I can't input a mass (the cell is greyed and I can't edit it) in the section property manager as shown on the attached picture.

Anyone came across that problem before?

am I missing a patch or a version?

Thanks for your help !