Genbi: Usage of operation "concatenate" followed by "split" and "group" results in a List<string> and not an array of string

[Seddryck]

Following code

case add column 'perspective_ticket' values '/93387';
case concatenate column 'ticket' with column 'perspective_ticket';
case split column 'ticket' with value '/';
case group column 'ticket';

applied to this template

<category>$ticket; separator="</category>
<category>"$</category>

results into following category:

<category>System.Collections.Generic.List`1[System.String]</category>