ckati differs from make when appending a variable to itself

[Colin Cross]

ckati fails this testcase:
x := one
x += two $(x)
$(info $(x))

$ ./runtest.rb -c testcase/append_self_reference.mk
append_self_reference.mk: FAIL
--- out.make 2016-03-08 17:46:40.017690761 -0800
+++ out.kati 2016-03-08 17:46:40.017690761 -0800
@@ -1,5 +1,5 @@
=== ===
-one two one
+one two one two
*** No targets.

=== FILES ===

=== Failures ===
append_self_reference.mk

FAIL! (1 fails 0 passes)