This patch is submitted upstream as:

bug #36106: make target-specific variables fail if over 150 characters and contain semicolon
http://savannah.gnu.org/bugs/index.php?36106

--- a/read.c	2010-07-13 03:20:42.000000000 +0200
+++ b/read.c	2012-04-05 23:25:12.155011371 +0200
@@ -1071,12 +1071,12 @@
                after it.  */
             if (semip)
               {
-                unsigned int l = p - variable_buffer;
+                unsigned int l = p2 - variable_buffer;
                 *(--semip) = ';';
                 collapse_continuations (semip);
                 variable_buffer_output (p2 + strlen (p2),
                                         semip, strlen (semip)+1);
-                p = variable_buffer + l;
+                p2 = variable_buffer + l;
               }
             record_target_var (filenames, p2,
                                vmod.override_v ? o_override : o_file,