Ordinary worksheets use natural recalculation. This means that Fireworkz builds a tree of dependencies and uses this dependency tree to determine the order of recalculation. Custom function sheets are recalculated differently, with recalculation proceeding down the worksheet from one row to the next.
The only links between the worksheet and the custom function sheet are the function name definition cells. Each of these cells is known about by the dependency tree, but none of the rest of the custom function is put on the dependency tree.
For this reason you should make not references into a custom function sheet from an external worksheet and you should not make references from a custom function sheet to an external worksheet. All of the data needed by a custom function should be passed into the function as function parameters. All of the data which the function exports should be passed out using RESULT
, perhaps passing out an array.