synchronous messages don't advance in sequence diagram

Hi.

I use Umbrello 1.5.4 in KDE 3.5.4 (FreeBSD 6.1).

I have a question about synchronous message's returning arrow, if you know 
what I mean ;)

How do I extend the duration of it so that several messages (system calls) 
would be started in sequence, not just by themselves (starting after the 
previous has ended in the timeline).

I just can't achieve a diagram showed in page: 
http://www.visualcase.com/tutorials/interaction-diagrams.htm (search 
for "Sequence Diagrams" ;)

Is it bug in my system or it really can't be done?

Silver

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