diff --git a/CHANGES b/CHANGES
index 15a7296edc..0edbf4375b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,4 +1,8 @@
 
+4.1.0-dev.501 | 2021-04-12 18:03:53 -0700
+
+  * Add explanation of vector holes/in-operator changes to NEWS (Jon Siwek, Corelight)
+
 4.1.0-dev.500 | 2021-04-09 12:18:06 -0700
 
   * Reference the manual's explanation of originator and responder from conn_id (Christian Kreibich, Corelight)
diff --git a/NEWS b/NEWS
index 58d705863c..bbc673ba15 100644
--- a/NEWS
+++ b/NEWS
@@ -52,6 +52,19 @@ New Functionality
 Changed Functionality
 ---------------------
 
+- The ``in`` operator does not any more track whether a given vector element
+  has been assigned too. It now simply equates to "is this index between zero
+  and the size-of-the-vector-minus-one, inclusive".  Previously, the ``in``
+  operator could have detected whether, by purpose or accident, a "hole" was
+  created in a vector by way of assigning to an index that's more than 1 beyond
+  the end of the vector (with intermediate elements becoming "holes") and
+  whether a "hole" had ever been subsequently filled by an assignment.
+
+  The behavior of creating a "hole" in a vector was never explicitly
+  documented, and should be thought of as undefined behavior and not something
+  the ``in`` operator can be used to detect.  For this kind of usage, a
+  ``table[count] of X`` is more appropriate than a vector.
+
 Removed Functionality
 ---------------------
 
diff --git a/VERSION b/VERSION
index c9ca2f3a9f..92c6e9a1f2 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-4.1.0-dev.500
+4.1.0-dev.501