Make sure to use threads result cached in-memory for correct folder

program/lib/Roundcube/rcube_imap.php

@@ -812,7 +812,12 @@ class rcube_imap extends rcube_storage
             return $mcache->get_thread($folder);
         }
 
-        if (empty($this->icache['threads'])) {
+        if (!empty($this->icache['threads'])) {
+            if ($this->icache['threads']->get_parameters('MAILBOX') == $folder) {
+                return $this->icache['threads'];
+            }
+        }
+
         if (!$this->check_connection()) {
             return new rcube_result_thread();
         }
@@ -822,10 +827,7 @@ class rcube_imap extends rcube_storage
             $this->options['skip_deleted'] ? 'UNDELETED' : '', true);
 
         // add to internal (fast) cache
-            $this->icache['threads'] = $result;
+        return $this->icache['threads'] = $result;
-        }
-
-        return $this->icache['threads'];
     }