Conversion of compound units gives wrong result

[shrdlu9-lab]

I noticed that converting some compound units from SI/US produces wrong results.
Here is an example with mass per area:

var qty = new Qty(657.5, 'kg/m^2');
qty.to('lb/sqft');

This results in 1449.54lbs/sqft.
The correct result would be 134.6lbs/sqft.

Other examples include a unit of enthalpy 'kJ/m^2' converted to 'BTU/sqft'.
I assume this is due to wrong grouping: is there another way I can write the units so it will work?