Excel 2007 : Incorrect sumproduct with random numbers

[Mark@Work]

I was fiddling with ideas in conection with a post in the miscellaneous group (Huwbob's problem "Check instances of values in a column") using the attached sheet.
To generate a set of numbers to work with I used RANDBETWEEN(0,10), I was then using SUMPRODUCT to determine the number of times any of three numbers appeared in the randomly generated list.
Regardless of whether this is a sensible way of solving the problem, I encountered an unexpected effect.

I noticed that as I re-calculated the random numbers, the result was not changing.
I stepped through the calculation using the "Evaluate Function" feature, and the calculations are correct, until the final step!
Note that if I use copy and paste-special values to replace the random number formulas with the numeric values, the calculation is correct.
Any Ideas? (I am using Office 2007)

Mark.

[Mark@Work]

I think I have identified why the problem occurs.
EXCEL "sees" that none of the cells upon which the errant formula depends have been altered, so it does not refresh the value.
If I change any one of the precedent cells, the formula refreshes correctly.
Although the value of the random numbers has changed, the formula in the cell remains the same, so EXCEL does not flag its dependents as requiring recalculation.
Does this happen with other calculations based on the random number functions?

Mark.