The two braces uses faces that look identical, but they are indeed
different faces.  The following patch fixes the test case, but I don't
really know Objective Pascal at all.  For reference, this is what
pascal.el says about comments:

  (setq-local comment-start "{")
  (setq-local comment-start-skip "(\\*+ *\\|{ *")
  (setq-local comment-end "}")

I've added Simon the the CCs; perhaps he has some insight here.

diff --git a/lisp/progmodes/opascal.el b/lisp/progmodes/opascal.el
index 662d2b4b74..686e72ce6d 100644
--- a/lisp/progmodes/opascal.el
+++ b/lisp/progmodes/opascal.el
@@ -1766,6 +1766,7 @@ opascal-mode
   (setq-local syntax-propertize-function opascal--syntax-propertize)
 
   (setq-local comment-start "// ")
+  (setq-local comment-end "}")
   (setq-local comment-start-skip "\\(?://\\|(\\*\\|{\\)[ \t]*")
   (setq-local comment-end-skip "[ \t]*\\(?:\n\\|\\*)\\|}\\)"))
 

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no