When querying the value of a property that has custom units, there is no way to get an 'unformatted' value returned by the query.
Specifically, numbers are always full of commas (e.g. 10,004,039) and the value is always attached to a unit (separated by an " ").
I think the 'natural' way to do this would be to specify "Plain (unformatted) printouts" for the property in question
However, SMW insists on putting commas in large numbers  and outputting a unit and putting a " " between the printed value and the unit.
All nice ideas in principle, but the whole point of SMW is to provide *data* not *formatting*. Currently you can't get at the underlying data, to include it in a calculation, for example, so this is a bug.
This bug is different from but related to bug 15541.