diff --git a/CIME/SystemTests/eri.py b/CIME/SystemTests/eri.py
index f0a237b6819..597cfe4c709 100644
--- a/CIME/SystemTests/eri.py
+++ b/CIME/SystemTests/eri.py
@@ -223,6 +223,15 @@ def run_phase(self):
         # (3a) Test run:
         # do a branch run from ref2 restart (short term archiving is off)
         #
+        # One aspect of this branch run worth noting is that it writes an extra set of
+        # restart files in the middle of the run, which are not written in the reference
+        # case. (These restart files are needed for the final continue run.) This is one
+        # of the few (or only) instances in the CIME System Tests where we do a comparison
+        # between two runs where one run has written an extra set of restart files
+        # part-way through. This can catch a particular type of error that arises
+        # occasionally: where the mere act of *writing* a restart file can change answers.
+        # (See also the discussion in https://github.com/ESMCI/cime/issues/4859.)
+        #
 
         os.chdir(caseroot)
         self._set_active_case(orig_case)
diff --git a/doc/source/system_testing.rst b/doc/source/system_testing.rst
index 94804b2da47..24b08f35e63 100644
--- a/doc/source/system_testing.rst
+++ b/doc/source/system_testing.rst
@@ -243,6 +243,14 @@ TESTTYPE     Description
                 Do a branch run, starting from restarts written in ref2case,
                 for 9 days and writing restarts at day 5.
                 Short term archiving is off.
+
+                One aspect of this branch run worth noting is that it writes an extra set of
+                restart files in the middle of the run, which are not written in the reference
+                case. (These restart files are needed for the final continue run.) This is one
+                of the few (or only) instances in the CIME System Tests where we do a comparison
+                between two runs where one run has written an extra set of restart files
+                part-way through. This can catch a particular type of error that arises
+                occasionally: where the mere act of *writing* a restart file can change answers.
               case - restart (Suffix rest)
                 Do a restart run from the branch run restarts for 4 days.
                 Short term archiving is off.