diff -u b/core/lib/Drupal/Core/TypedData/TypedDataManager.php b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
--- b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
+++ b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
@@ -256,8 +256,7 @@
     // We consider we can reuse an existing prototype if it was built:
     // - for the same runtime $definition object,
     // - and for the same parent hiararchy.
-    $key = spl_object_hash($definition) . '.';
-    $key .= ':' . $object->getPropertyPath() . '.';
+    $key = spl_object_hash($definition) . '.' . $object->getPropertyPath() . '.';
     // If we are creating list items, we always use 0 in the key as all list
     // items look the same.
     $key .= is_numeric($property_name) ? 0 : $property_name;