CCSID(*CHAR:*UTF8) and %SUBSTR on 7.2

On a 7.2 machine I can use the new keyword CCSID(*CHAR:*UTF8), defining my
char variables with ccsid 1208.
It seems to me that %subst does not substring characters, but bytes.

I'm running some tests, and i obtain these results.
My job ccsid is 1144.
I assign the string '€' (euro sign) to my utf-8 variable CHAR10.

H DECEDIT(*JOBRUN) DATEDIT(*DMY/) DFTACTGRP(*NO) ACTGRP(*CALLER)
H OPTION(*NODEBUGIO)
H CCSID(*UCS2: 1200)
H CCSID(*CHAR:*UTF8)
*
D CHAR10 S 10
D RTCHA1 S 10
D RTCHA2 S 10
D RTCHA3 S 10
C EVAL CHAR10='€'
C EVAL CHAR20=TXT(1)
C EVAL RTCHA1=%SUBST(CHAR10:1:1)
C EVAL RTCHA2=%SUBST(CHAR10:1:2)
C EVAL RTCHA3=%SUBST(CHAR10:1:3)
C EVAL *INLR=*ON

The euro sign hex is E282AC (3 bytes).
If I try to substring CHAR10 I obtain this:
C EVAL RTCHA1=%SUBST(CHAR10:1:1)
RTCHA1 = 'S■■■■■■■■■' hex 'E2202020 20202020 2020'

C EVAL RTCHA2=%SUBST(CHAR10:1:2)
RTCHA2 = 'Sb■■■■■■■■' hex 'E2822020 20202020 2020'

C EVAL RTCHA3=%SUBST(CHAR10:1:3)
RTCHA3 = '€ ' hex 'E282AC20 20202020 2020'

So it seems that %subst does not substring characters, but bytes.
I'm doing something wrong or this is working as expected?
How can I substring CHAR10?
Thanks for any advice.

Marco