diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt
index e98a8c658e5..1e69f54d041 100644
--- a/release_docs/RELEASE.txt
+++ b/release_docs/RELEASE.txt
@@ -1434,6 +1434,9 @@ Known Problems
     CPP ptable test fails on both VS2017 and VS2019 with Intel compiler, JIRA
     issue: HDFFV-10628.  This test will pass with VS2015 with Intel compiler.
 
+    The subsetting option in ph5diff currently will fail and should be avoided.
+    The subsetting option works correctly in serial h5diff.
+
     Known problems in previous releases can be found in the HISTORY*.txt files
     in the HDF5 source. Please report any new problems found to
     help@hdfgroup.org.