2. Different Valuation Areas means you have differents accounting: IFRS, HGB, GAAP etc. So different VA cash flow means different postings.
As concerns Security account class:
This cash flow displays all the planned or executed flows for a class in a securities account in chronological order.
These flow records can be generated in various ways:
■ Flows entered manually (investment amounts, charges, unscheduled repayments)
■ Flow records (as a rule generated from the conditions)
■ Accrual/deferral flows that result from the periodic assignment of outgoing and incoming payments
■ Valuation flows (for example, price gains and losses)
postings for sec.acc.class is debit position.
see: help.sap.com