The ComposeWorkflowOperationHandler allows users to specify both source-flavor (or source-flavors) and source-tags. The operation assumes that the tracks with either matching flavor or tags should be selected.
However, there are cases where the tags could be used to filtering rather than selecting tracks. For instance, when there are several copies of the same track with the same flavor but different tags to tell them apart.
My suggestion is to include a new parameter that allows the workflow designer to select the behaviour regarding the track selection: whether a track should match either the provided flavor(s) or tags (as it is already the case) or both the provided flavors and tags (read: any of the provided flavors and any of the provided tags).