FIX: Never show the last read marker within 1 post of the last

app/assets/javascripts/discourse/components/topic-progress.js.es6

@@ -39,9 +39,11 @@ export default Ember.Component.extend({
 
   @computed('progressPosition', 'topic.last_read_post_id')
   showBackButton(position, lastReadId) {
-    if (!this.site.mobileView || !lastReadId) { return; }
-    const readPos = this.get('postStream.stream').indexOf(lastReadId) || 0;
-    return readPos > position;
+    if (!lastReadId) { return; }
+
+    const stream = this.get('postStream.stream');
+    const readPos = stream.indexOf(lastReadId) || 0;
+    return (readPos < (stream.length - 1)) && (readPos > position);
   },
 
   @observes('postStream.stream.[]')

app/assets/javascripts/discourse/widgets/topic-timeline.js.es6

@@ -165,6 +165,7 @@ createWidget('timeline-scrollarea', {
     const hasBackPosition =
       position.lastRead > 3 &&
       Math.abs(position.lastRead - position.current) > 3 &&
+      Math.abs(position.lastRead - position.total) > 1 &&
       (position.lastRead && position.lastRead !== position.total);
 
     if (hasBackPosition) {

app/assets/stylesheets/desktop/topic.scss

@@ -87,6 +87,19 @@
   width: 757px;
 }
 
+.progress-back-container {
+  position: fixed;
+  width: 0;
+  right: 0;
+  bottom: 40px;
+  z-index: 950;
+  margin-right: 105px;
+
+  .btn {
+    margin: 0;
+  }
+}
+
 #topic-progress-wrapper {
   position: fixed;
   right: 50%;

app/assets/stylesheets/mobile/topic.scss

@@ -61,19 +61,6 @@
   margin-right: 148px;
 }
 
-.progress-back-container {
-  position: fixed;
-  width: 0;
-  right: 0;
-  bottom: 40px;
-  z-index: 950;
-  margin-right: 105px;
-
-  .btn {
-    margin: 0;
-  }
-}
-
 #topic-progress-expanded {
   border: 1px solid dark-light-diff($primary, $secondary, 90%, -60%);
   padding: 5px;