diff --git a/frontend/src/stores.js b/frontend/src/stores.js
index 3305f87..6594fc1 100644
--- a/frontend/src/stores.js
+++ b/frontend/src/stores.js
@@ -14,6 +14,10 @@ class Store {
         this.name = name;
     }
 
+    log(...e) {
+        return storeLog(`[${this.name}]`, ...e);
+    }
+
     // like subscribe, but without initially calling the handler
     watch(handler) {
         storeLog(`[Watch] (${this.name})`, "handler:", handler);
@@ -174,15 +178,18 @@ class MessageStore extends Store {
     }
 
     _recomputeMessages() {
+        const start = performance.now();
         for (let i = 0; i < this.value.length; i++) {
             this.value[i] = this._processMessage(this.value[i], this.value[i - 1]);
         }
+        const delta = performance.now() - start;
+        this.log(`[_recomputeMessages] Computed ${this.value.length} messages in ${delta}ms`);
     }
 
     _processMessage(message, previous=null) {
-        message._createdAtDate = new Date(parseInt(message.created_at));
-        message._createdAtTimeString = new Intl.DateTimeFormat(getItem("ui:locale"), { hour: "numeric", minute: "numeric" }).format(message._createdAtDate);
-        message._createdAtDateString = message._createdAtDate.toLocaleDateString();
+        message._createdAtDate = message._createdAtDate || new Date(parseInt(message.created_at));
+        message._createdAtTimeString = message._createdAtTimeString || new Intl.DateTimeFormat(getItem("ui:locale"), { hour: "numeric", minute: "numeric" }).format(message._createdAtDate);
+        message._createdAtDateString = message._createdAtDateString || message._createdAtDate.toLocaleDateString();
         message._mentions = false;
         message._editable = false;
         message._clumped = false;
@@ -196,7 +203,7 @@ class MessageStore extends Store {
         if (previous && (message._createdAtDate.getTime() - previous._createdAtDate.getTime()) <= 100 * 1000 && message.author_id === previous.author_id) {
             message._clumped = true;
         }
-        if (!previous || (previous._createdAtDateString !== message._createdAtDateString)) {
+        if (!previous || (previous._createdAtDateString !== message._createdAtDateString && !message._aboveDateMarker)) {
             message._aboveDateMarker = new Intl.DateTimeFormat(getItem("ui:locale"), { month: "long", day: "numeric", year: "numeric" }).format(message._createdAtDate);
         }
         return message;