Masternodes are called "Hybrid Masternodes" for this reason, because you are receiving 33% of both Proof of Work and Proof of Stake blocks.
So completely normal and expected. One can certainly hope to get more PoW block rewards over PoS generally, but that is also depending on what others are staking

That is strange to hear such a hybrid masternodes. Will the MN payment mechanism remain constantly all the time or will it change at specific block in the future?