Thanks Renatas, but our company is not using derived flows.
I have found out that if I untick relevant to posting in the flow type definition of money market, the extra cash flow will be generated. But if I tick the option, the flow disappear and everything looks fine.
However, I do not need FI postings for this business scenario and this behavior of SAP is rather strange to me.
I'm going to log to OSS to find out if this is a bug and if there's any note we can apply.
Thanks.
Sei