Yes, it is strange. But remember, that the AMOUNTS paid were not changed. StakeV8 only indirectly affects, WHEN you will be paid the interest or BOINC reward. If you average it over long time, it should be the same (assuming no transactions happen, which destroy interest, etc).
The formula for interest is and was Tx.Value*Tx.Age*InterestRate, which is also called Coin*Age interest. (assuming correct units).