Concatenate User for Expression

["Schröder, Ute Marion"]

Hello,
 
I believe it has to be quite a simple task but right now I=B4m totally =
lost.
I have an element in my workflow container called UNAME
now I use a step to concatenate a user-id (retrieved from a table in a
previous step)
and US into the container elment UNAME.
 
        data:      personresponsible type csks-verak .
 
          swc_get_element container 'UNAME' personresponsible.
 
        concatenate 'US' personresponsible(18) into personresponsible.
          swc_set_element container 'UNAME' personresponsible.
 
But if I take a look at the container after this step,
element User just contains US and not the rest of the string.
I tested the coding in Abap an the concatenation works fine.
 
What am I missing?
 
Thankx for your help and patience
 
 
> Ute