I'm trying to force loading modules which are already present on the page. This works only if allowRollup is set to true and fails if it is false. The problem seems to be caused by forceMap property
initialized in _rollup method only; however, it is used in _reduce anyway:

                if (((this.loaded[i] || ON_PAGE[i]) &&

                        !this.forceMap[i] && !this.ignoreRegistered) ||

                        (type && m && m.type != type)) {

See attached example for demonstration.