Siemens Spring Clip and Bus Bar not compatible!
@samzun - very frustrating, it seems like you're doing your homework and still you have this problem.  It's very good that you caught it though.  

I can only see three possibilities:  


Someone at Siemens made a mistake confirming compatibility of this
breaker.  I do not believe this to be the case, but Siemen's web
site and literature are not really helpful.  If this is the case,
I'd expect Siemens to provide the correct breaker.   
The breaker is
defective.  (Since other breakers fit, I doubt the panel bus is
defective.)  Again I'd expect a warranty replacement either from the
retailer or the manufacturer.   
The breaker is a counterfeit.  You
might get a refund from the retailer, but I'd bring it to Siemens
attention.  Siemens and other manufacturers are very interested in
stopping counterfeiters.  See this document from Siemens: Counterfeit 
Circuit Breakers: A Growing Threat


If I can make a suggestion, in this and other questions, you are struggling quite a bit working with your panel bus.  It might make more sense to use DIN rail mountable breakers which are commonly used in Europe.  There's no bus with this system.  This seems to me a much easier way to retrofit GFCI protection with your panel.  For example look at the Eaton QPGF2030 or QPHGF2030 breakers.