Trouble with quotes in comments for mode derived from sql-mode

[address@hidden]

Hello,

I've written a very simple derived mode 'isq' mode which adds c++ style
comments
to sql-mode. The problem am having is unbalanced quotes in comments
mess up string
highlighting. I've seen similar problems in this group but haven't
found a solution.

Here's my derived mode:

(define-derived-mode isq-mode sql-mode "ISQ" "Major mode to edit Sybase
ISQ files."
  (setq indent-tabs-mode nil)
  (setq comment-start "// ")
)

(font-lock-add-keywords 'isq-mode '(("\\(--.*\\|//.*\\)$" (0
'font-lock-comment-face t))))
(add-to-list 'auto-mode-alist '(".isq\\'" . isq-mode))

I'm not sure if this is a shortcoming of sql-mode itself or if I'm
missing something.
Any help would be appreciated.

I'm using gnu emacs 21.1.1 on solaris 2.8

-Colin