This is somehow expected, as the value (as far as I got it) is combined of: Fixed amount of BTC from past rounds + variable (changing/proportional) amount of BTC from this round. Every time a round ends, the value kinda gets frozen and on top of that, the new variable amount is placed.

Example: .30 BTC from previous rounds, this round I have 1% of shares (=0.50 BTC) --> ~0.80 BTC displayed. As soon as a block is found, I still continue to have 1% of hashing power, so I still have 1% of shares --> ~1.30 BTC displayed. If I stopped immediately after a few shares, this value would go down to a minimum of ~0.80BTC again over time, as others are still producing shares, but I am no longer doing that.