Query plan cache bloated by ad-hoc queries, even with "Optimize for Ad-hoc Workloads"
According to this, the second run of an ad hoc batch removes the stub (which was used only once) and creates and caches the plan (using it for the first time).

I also haven't seen many references to refcounts other than it being a count of references by cache objects. Adhoc Compiled Plan objects can still have a refcount of 1, so it's not exclusively caused by the persistence of the plan.