Add a more clear note about query builder caching (issue #2721)
diff --git a/user_guide_src/source/database/query_builder.rst b/user_guide_src/source/database/query_builder.rst
index 9a96db0..5bfdfdb 100644
--- a/user_guide_src/source/database/query_builder.rst
+++ b/user_guide_src/source/database/query_builder.rst
@@ -1058,4 +1058,9 @@
$data = $this->db->get()->result_array();
// Would execute and return an array of results of the following query:
- // SELECT field1, field1 from mytable where field3 = 5;
\ No newline at end of file
+ // SELECT field1, field1 from mytable where field3 = 5;
+
+.. note:: Double calls to ``get_compiled_select()`` while you're using the
+ Query Builder Caching functionality and NOT resetting your queries
+ will results in the cache being merged twice. That in turn will
+ i.e. if you're caching a ``select()`` - select the same field twice.
\ No newline at end of file