I'm seeing a lot of issues with weldments in BoMs since upgrading from 2013 to 2016. We have weldment parts with multiple structural members that are used in subassemblies. Those subassemblies are set to promote. On the top level assembly drawing, we use an indented parts list with flat numbering. Previously in 2013, all of the structural members combined properly and displayed the total length, part number and description. Since upgrading to 2016, the structural member descriptions do not display properly when combined with structural members from another weldment part.
I have created a simple assembly and drawing to illustrate this problem (see attached). When both weldments are dissolved, the description for the p/n 10000 square tube changes from "TUBE, SQUARE 2.00 X 2.00 X .25" to "PIPE, SCH 40, 1.00 DIA.". This is the only structural member that is shared between both weldment parts. I have similar assemblies that completely loose their descriptions when combined. I also have problems dissolving weldment parts and usually have to replace the bom to get the parts to dissolve.