sum serves for simplifying symbolic sums (the discrete analog of integration). It should not be used for simply adding a finite number of terms: if a and b are integers of type DOM_INT, the call _plus(f $ i = a..b) gives the desired result, while sum(f, i = a..b) may return unevaluated. expand may be used to sum such an unevaluated finite sum. See example 3.
As your qir are known (arbitrary) numeric values rather than formula, you are encountering exactly the above case where symsum() should not be used.
