upgrade/v2312-User-Upgrade-Guide.md

@@ -19,6 +19,15 @@
 
 ## Input Dictionaries
 
+## Changes in behaviour
+
+### Function object: `Lambda2`
+
+The output of the `Lambda2` function object has been corrected through an
+alteration in the governing equation, specifically by reversing its sign.
+Consequently, the negative field values observed in the pre-`v2312` version of
+`Lambda2` are now rendered positive (and vice versa) in the `v2312` release.
+
 ----
 
 [code-patterns]: /coding/patterns/patterns