UTF-8 display problem

Hi,
I use 1.2 with UTF-8 charset for vietnamese. All HTML headers have :

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

When I type in TEXTAREA, I see correct characters:

When I do "Preview" it's ok too:

But when I do "Submit" the result was not correct:

The following characters have problem:
00E0, 00C1  (See http://www.unicode.org/charts/PDF/U0080.pdf)
1EA0, 1ECF, 1ECD (see http://www.unicode.org/charts/PDF/U1E00.pdf)

With punBB 1.1.5 I have not this problem. All vietnamese UTF-8 characters were correctly presented.

Any ideas for help ?
Thank you in advance,