BufferingTable does not provide an easy way to merge any pending writes in the buffer with the results of a multi-get request.
BufferingTable should define an abstract method:
public abstract List<Row> getPersisted(List<Get> gets);
and override the method get(List<Get>), delegating to getPersisted() for the persisted results, then merging any results from the buffer back on to the response.
Or, alternately, BufferingTable could provide a protected method for subclasses to access the contents of the buffer per-row, allowing the subclasses to merge the buffered and persisted results.