diff --git a/ANNOUNCE b/ANNOUNCE
index 43355ac01..765f99f8f 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,5 +1,5 @@
 
-Libpng 1.5.10beta04 - March 6, 2012
+Libpng 1.5.10beta04 - March 9, 2012
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -50,8 +50,11 @@ Version 1.5.10beta03 [March 6, 2012]
     of png_ptr->current_text from pngread.c
   Added palette-index checking.
 
-Version 1.5.10beta04 [March 6, 2012]
+Version 1.5.10beta04 [March 9, 2012]
   Fixed PNG_LIBPNG_BUILD_BASE_TYPE definition.
+  Disabled part of the CMF optimization of non-IDAT compressed chunks, which
+    was added at libpng-1.5.4.  It sometimes produces too small of a window.
+    This has been fixed in libpng-1.6.0.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index 93ddbb545..0e48894a6 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3835,8 +3835,11 @@ Version 1.5.10beta03 [March 6, 2012]
     of png_ptr->current_text from pngread.c
   Added palette-index checking.
 
-Version 1.5.10beta04 [March 6, 2012]
+Version 1.5.10beta04 [March 9, 2012]
   Fixed PNG_LIBPNG_BUILD_BASE_TYPE definition.
+  Disabled part of the CMF optimization of non-IDAT compressed chunks, which
+    was added at libpng-1.5.4.  It sometimes produces too small of a window.
+    This has been fixed in libpng-1.6.0.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/pngwutil.c b/pngwutil.c
index da18e9502..d8c00dc15 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -619,6 +619,7 @@ png_write_compressed_data_out(png_structp png_ptr, compression_state *comp)
          if (comp->num_output_ptr)
          {
 
+#if 0 /* The following sometimes produces incorrect zlib datastreams */
            if (comp->output_ptr[0][0] != z_cmf)
            {
               int tmp;
@@ -628,6 +629,7 @@ png_write_compressed_data_out(png_structp png_ptr, compression_state *comp)
               tmp += 0x1f - ((z_cmf << 8) + tmp) % 0x1f;
               comp->output_ptr[0][1] = (png_byte)tmp;
            }
+#endif /* 0 */
          }
          else
          {