diff --git a/src/services/workflow.service.js b/src/services/workflow.service.js
index b1ec1b032b..d096123f9b 100644
--- a/src/services/workflow.service.js
+++ b/src/services/workflow.service.js
@@ -16,7 +16,7 @@
  */
 
 import isEqual from 'lodash/isEqual'
-import union from 'lodash/union'
+import unionBy from 'lodash/unionBy'
 import ViewState from '@/model/ViewState.model'
 import Subscription from '@/model/Subscription.model'
 import {
@@ -324,7 +324,9 @@ class WorkflowService {
         throw new Error('Error recomputing subscription: Query variables do not match.')
       }
       this.mergeQueries(baseSubscriber.query.query, subscriber.query.query)
-      subscription.callbacks = union(subscription.callbacks, subscriber.query.callbacks)
+      // Combine the arrays of callbacks, creating an array of unique callbacks.
+      // The callbacks are compared by their class/constructor name.
+      subscription.callbacks = unionBy(subscription.callbacks, subscriber.query.callbacks, (callback) => callback.constructor.name)
     }
     const finalQuery = print(baseSubscriber.query.query)
     // TODO: consider using a better approach than print(a) === print(b)
diff --git a/tests/unit/services/workflow.service.spec.js b/tests/unit/services/workflow.service.spec.js
index bebb4c0f33..6d953b067b 100644
--- a/tests/unit/services/workflow.service.spec.js
+++ b/tests/unit/services/workflow.service.spec.js
@@ -35,6 +35,13 @@ const sandbox = sinon.createSandbox()
 
 Vue.use(Vuex)
 
+if (!global.localStorage) {
+  global.localStorage = {
+    getItem () { return '{}' },
+    setItem () {}
+  }
+}
+
 describe('WorkflowService', () => {
   /**
    * @type {String}
@@ -264,7 +271,7 @@ describe('WorkflowService', () => {
       const finalQuery = print(service.subscriptions.root.query.query)
       expect(expectedQuery1).to.equal(finalQuery)
     })
-    it('should not add duplicate action names', () => {
+    it('should not add duplicate callbacks', () => {
       const newCallbacks = [
         new WorkflowCallback(),
         new TreeCallback()
@@ -281,10 +288,10 @@ describe('WorkflowService', () => {
         query: newSubscriptionQuery
       }
       service.subscribe(anotherView)
-      // Same action names, Lodash's union should add to list like a set
+      // Same callbacks, Lodash's union should add to list like a set
       expect(subscriptionQuery.callbacks).to.deep.equal(newCallbacks)
     })
-    it('should add new action names', () => {
+    it('should add new callbacks', () => {
       const baseCallbacks = [new WorkflowCallback()]
       subscriptionQuery.callbacks.push(...baseCallbacks)
       const newCallbacks = [new TreeCallback()]
@@ -299,7 +306,7 @@ describe('WorkflowService', () => {
         query: newSubscriptionQuery
       }
       service.subscribe(anotherView)
-      // Same action names, Lodash's union should add to list like a set
+      // Same callbacks, Lodash's union should add to list like a set
       expect(subscription.callbacks).to.deep.equal([...baseCallbacks, new TreeCallback()])
     })
     it('should throw an error if there are no subscribers', () => {