diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/room/timeline/TimelineEvent.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/room/timeline/TimelineEvent.kt
index 7010a80233..32f6b94cd8 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/room/timeline/TimelineEvent.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/room/timeline/TimelineEvent.kt
@@ -38,6 +38,9 @@ import org.matrix.android.sdk.api.util.ContentUtils.extractUsefulTextFromReply
  */
 data class TimelineEvent(
         val root: Event,
+        /**
+         * Uniquely identify an event, computed locally by the sdk
+         */
         val localId: Long,
         val eventId: String,
         val displayIndex: Int,
diff --git a/vector/src/main/java/im/vector/app/features/home/room/detail/timeline/TimelineEventController.kt b/vector/src/main/java/im/vector/app/features/home/room/detail/timeline/TimelineEventController.kt
index 9acd34c827..41d9fd6de2 100644
--- a/vector/src/main/java/im/vector/app/features/home/room/detail/timeline/TimelineEventController.kt
+++ b/vector/src/main/java/im/vector/app/features/home/room/detail/timeline/TimelineEventController.kt
@@ -427,6 +427,7 @@ class TimelineEventController @Inject constructor(private val dateFormatter: Vec
             val formattedDayModel: DaySeparatorItem? = null
     ) {
         fun shouldTriggerBuild(): Boolean {
+            // Since those items can change when we paginate, force a re-build
             return mergedHeaderModel != null || formattedDayModel != null
         }
     }