Custom property for BOM

I'm trying to set up the bill of materials so that it canproduce a cutting list for welded assemblies not made using'weldments' - just using parts. To this end, as an experiment I'veset up a 'Rectangular Hollow Section' Part - with severalconfigurations.

In order to get the overall length I made a configuration specificcustom property 'length' - set it to 'text' and then clicked thelength dimension - the address of which went into the 'value'column.

I then opened a drawing - added two instances (differentconfigurations) and added a BOM. I added a new column and set itsproperty to 'length'. Sure enough it came up with the appropriatevalue.

However after saving and re-opening the numeric length has beenreplaced with the dimension reference in both the BOM and theproperties table?

Does anyone know if I'm doing something silly?

Thanks, DebbieSolidworksConfigurations design Tables