The fix isn't very trivial.  It would have to start by fixing
the documentation for that field:
Index: hivedata.h
===================================================================
--- hivedata.h  (revision 52019)
+++ hivedata.h  (working copy)
@@ -143,7 +143,9 @@
       If the hive is volatile, this is the actual pointer to the CM_KEY_NODE */
    HCELL_INDEX RootCell;
-   /* Size of each hive block ? */
+   /* Length of meaningful data in the file, excluding base block.
+      The file itself can be longer than this, but Windows will ignore
+      anything after. */
    ULONG Length;
    /* (1?) */
----------------------------------------------------------------------
I'm still setting up a ReactOS build environment.
Rich.
--
Richard Jones, Virtualization Group, Red Hat 
http://people.redhat.com/~rjones
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