Unfortunately, this is a shortcoming of Revit. The fault however is not with Worksets, but with Categories. Because Revit does not allow Subcategories to be used as Family Types, many have gotten out of the habit of using them appropriately (to indicate different component types within a family/project). Worksets have replaced them in handling this, but that isn't right either. Worksets are meant to delineate areas of responsibility (i.e. different disciplines, offices or individual designers within a project). So it is natural that a single Workset would govern a single object to preclude design conflicts.
TL;DR: Don't use Worksets for different item types, use Subcategories. Ever in-place model has a category, and every component of that model can have a subcategory assigned to it, which can be changed at any time.
