I believe I have a repro for incorrect behavior of the :default option in a pull. When the attribute's value is false , the default will override it:

(def client (d/client {:server-type :dev-local :system "dev"}))

; insert schema and entity
(let [_      (d/create-database client {:db-name "repro"})
      con    (d/connect client {:db-name "repro"})
      schema [{:db/ident       :account/name
               :db/valueType   :db.type/string
               :db/unique      :db.unique/identity
               :db/cardinality :db.cardinality/one}
              {:db/ident       :account/active?
               :db/valueType   :db.type/boolean
               :db/cardinality :db.cardinality/one}]
      acct   {:account/name    "test"
              :account/active? false}]
  (d/transact con {:tx-data schema})
  (d/transact con {:tx-data [acct]}))

; query without default
(let [con (d/connect client {:db-name "repro"})]
  (d/pull (d/db con)
          '[:account/name
            :account/active?]
          [:account/name "test"]))
; => :account{:name "test", :active? false}


; query with default
(let [con (d/connect client {:db-name "repro"})]
  (d/pull (d/db con)
          '[:account/name
            [:account/active? :default true]]
          [:account/name "test"]))
; => :account{:name "test", :active? true}